The Chemical Species of Aluminum Influences Its Paracellular Flux across and Uptake into Caco-2 Cells, a Model of Gastrointestinal Absorption

Aluminum, a colorful gamechanger: Uptake of an aluminum-containing food color in human cells and its implications for human health

Aluminum is added to many food colors to change their solubility. This study compares the aluminum-containing food color carmine with its aluminum-free version carminic acid (both E 120), hypothesizing that the addition of aluminum does not only change the color's solubility, but also its effects on human cells. We could show that carmine, but not carminic acid, is taken up by gastrointestinal Caco-2 and umbilical vein endothelial cells (HUVEC). Clear differences between gene expression profiles of Caco-2 cells exposed to carmine, carminic acid or control were shown. KEGG analysis revealed that carmine-specific genes suppress oxidative phosphorylation, and showed that this suppression is associated with neurodegenerative diseases such as Alzheimer and Parkinson disease. Furthermore, carmine, but not carminic acid, increased proliferation of Caco-2 cells. Our findings show that a food color containing aluminum induces different cellular effects compared to its aluminum-free form, which is currently not considered in EU legislation.

Aluminum and ABC transporter activity

Aluminum is the third most common element on Earth´s crust and despite its wide use in our workaday life it has been associated with several health risks after overexposure. In the present study the impact of aluminum salts upon ABC transporter activity was studied in the P-GP-expressing human blood-brain barrier cell line hCMEC/D3, in MDCKII cells overexpressing BCRP and MRP2, respectively, and in freshly isolated, functionally intact kidney tubules from Atlantic killifish (Fundulus heteroclitus), which express the analog ABC transporters, P-gp, Bcrp and Mrp2. In contrast to previous findings with heavy metals salts (cadmium(II) chloride or mercury(II) chloride), which have a strong inhibitory effect on ABC transporter activity, or zinc(II) chloride and sodium arsenite, which have a stimulatory effect upon ABC transport function, the results indicate no modulatory effect of aluminum salts on the efflux activity of the human ABC transporters P-GP, BCRP and MRP2 nor on the analog transporters P-gp, Bcrp and Mrp2.

Metal-Based Nanoparticles and Their Relevant Consequences on Cytotoxicity Cascade and Induced Oxidative Stress

Emerging nanoscience allows us to take advantage of the improved evolutionary components and apply today’s advanced characterization and fabrication techniques to solve environmental and biological problems. Despite the promise that nanotechnology will improve our lives, the potential risks of technology remain largely uncertain. The lack of information on bio-impacts and the absence of consistent standards are the limitations of using metal-based nanoparticles (mNPs) for existing applications. To analyze the role played by the mNPs physicochemical characteristics and tactics to protect live beings, the field of nanotoxicology nowadays is focused on collecting and analyzing data from in vitro and in vivo investigations. The degree of reactive oxygen species (ROS) and oxidative stress caused by material nanoparticles (NPs) depends on many factors, such as size, shape, chemical composition, etc. These characteristics enable NPs to enter cells and interact with biological macromolecules and cell organelles, resulting in oxidative damage, an inflammatory response, the development of mitochondrial dysfunction, damage to genetic material, or cytotoxic effects. This report explored the mechanisms and cellular signaling cascades of mNPs-induced oxidative stress and the relevant health consequences.

Aluminum neurotoxicity and autophagy: a mechanistic view

It is strongly believed that aluminum is one of the insalubrious agents because of its neurotoxicity effects and influences on amyloid β (Aβ) production and tau protein hyperphosphorylation following oxidative stress, as one of the initial events in neurotoxicity. The autophagy process plays a considerable role in neurons in preserving intracellular homeostasis and recycling organelles and proteins, especially Aβ and soluble tau. Thus, autophagy is suggested to ameliorate aluminum neurotoxicity effects, and dysfunction of this process can lead to an increase in detrimental proteins. However, the relationship between aluminum neurotoxicity and autophagy dysregulation in some dimensions remains unclear. In the present review, we want to give an overview of the autophagy roles in aluminum neurotoxicity and how dysregulation of autophagy can affect aluminum neurotoxicity.

Aluminum induced intestinal dysfunction via mechanical, immune, chemical and biological barriers

Aluminum is the most abundant metal element in the Earth's crust, which exists naturally in the form of aluminum compounds. Aluminum is mainly absorbed through the gastrointestinal tract, which varies with different aluminum compounds. During this process, aluminum could induce the disruption of intestinal mucosa barrier. However, its underlying mechanism has not been elucidated yet. Previous studies have reported that aluminum can firstly promote the apoptosis of intestinal epithelial cells, destroy the structure of tight-junction proteins, and increase the intestinal permeability, injuring the mechanical barrier of gut. Also, it can induce the activation of immune cells to secrete inflammatory factors, and trigger immune responses, interfering with immune barrier. Moreover, aluminum treatment can regulate intestinal composition and bio-enzyme activity, impairing the function of chemical barrier. In addition, aluminum accumulation can induce an imbalance of the intestinal flora, inhibit the growth of beneficial bacteria, and promote the proliferation of harmful bacteria, which ultimately disrupting biological barrier. Collectively, aluminum may do extensive damage to intestinal barrier function covering mechanical barrier, immune barrier, chemical barrier and biological barrier.

Nanostructured lipid carriers with exceptional gastrointestinal stability and inhibition of P-gp efflux for improved oral delivery of tilmicosin

Tilmicosin (TMS) is widely applied to treat porcine bacterial respiratory diseases in veterinary medicine. However, oral administration of TMS is greatly limited due to its physicochemical properties, such as poor water solubility, gastric acid sensitivity and bitterness. Therefore, nanostructured lipid carriers (NLCs) were developed as an oral delivery system for TMS by the high shear method combined with ultrasonic techniques in this study. The results showed that TMS-NLCs were approximately spherical with a hydrodynamic diameter of 283.03 nm and a zeta potential of -30.04 mV. TMS was almost entirely encapsulated in the NLCs by interacting with the lipid matrix, as characterized by differential scanning calorimetry and fourier transform infrared spectroscopy. Thus, TMS-NLCs had an excellent encapsulation efficiency and loading capacity with values of 93.46% and 9.23%, respectively. TMS-NLCs maintained good stability not only during storage at 4 ℃, 25 ℃ and 40 ℃ for 90 days but also in stimulated gastrointestinal (GI) fluids at 37 ℃ for 7 days. Therefore, TMS-NLCs displayed low and sustained release in vitro without an initial burst release in stimulated GI fluids. Furthermore, TMS-NLCs showed higher oral bioavailability in piglets compared to the API suspension. Subsequently, Caco-2 cell monolayers were utilized to analyze the mechanism of NLC-enhanced oral adsorption of TMS. The data revealed that NLCs not only increased cellular uptake of TMS but also inhibited the efflux of P-gp in Caco-2 cells. Additionally, TMS-NLCs mainly entered Caco-2 cells via the caveolae/lipid raft-mediated endocytosis pathway. Moreover, nanoparticles were transported across Caco-2 cell monolayers in the intact form to the basolateral side, as identified by transmission electron microscopy, indicating that TMS-NLCs escape lysosome degradation. Taken together, these results indicate that NLCs are a potential delivery carrier for improving the solubility, permeability and oral bioavailability of TMS.

Aluminium toxicosis: a review of toxic actions and effects

Aluminium (Al) is frequently accessible to animal and human populations to the extent that intoxications may occur. Intake of Al is by inhalation of aerosols or particles, ingestion of food, water and medicaments, skin contact, vaccination, dialysis and infusions. Toxic actions of Al induce oxidative stress, immunologic alterations, genotoxicity, pro-inflammatory effect, peptide denaturation or transformation, enzymatic dysfunction, metabolic derangement, amyloidogenesis, membrane perturbation, iron dyshomeostasis, apoptosis, necrosis and dysplasia. The pathological conditions associated with Al toxicosis are desquamative interstitial pneumonia, pulmonary alveolar proteinosis, granulomas, granulomatosis and fibrosis, toxic myocarditis, thrombosis and ischemic stroke, granulomatous enteritis, Crohn's disease, inflammatory bowel diseases, anemia, Alzheimer's disease, dementia, sclerosis, autism, macrophagic myofasciitis, osteomalacia, oligospermia and infertility, hepatorenal disease, breast cancer and cyst, pancreatitis, pancreatic necrosis and diabetes mellitus. The review provides a broad overview of Al toxicosis as a background for sustained investigations of the toxicology of Al compounds of public health importance.

Bacopa phospholipid complex retrieves aluminum maltolate complex-induced oxidative stress and apoptotic alterations in the brain regions of albino rat

Highly bioavailable plant phospholipid complex that can reverse aluminum maltolate (AlM)-induced toxicity is not yet reported. Hence, the present study was planned to investigate the impact of oxidative stress and apoptotic changes provoked by Al and ameliorative role of Bacopa phospholipid complex (BPC) in albino rats. The levels of antioxidant enzymes such as superoxide dismutase (SOD), catalase activity (CAT), glutathione peroxidase (GPx), and thiobarbituric acid-reactive substance (TBA-RS) were measured and immunohistochemistry analysis of apoptotic markers, Bax and Bcl-2, was done from the four brain regions such as the hippocampus, cerebral cortex, cerebellum, and medulla oblongata. The levels of antioxidant enzymes and apoptotic markers that were decreased on AlM induction showed a significant increase in their levels, almost as observed in the control, when treated with BPC and Bm. Our results indicate that both BPC and Bm showed a therapeutic effect against AlM toxicity; however, it was found that the therapeutic potential of BPC was more pronounced than Bm against AlM-induced neurotoxicity.

Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells

Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different in vitro assays were performed to determine potential effects and molecular modes of action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al₂O₃ nanoparticles, while AlCl₃ showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 µg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.

Recent Progress in Metal-Based Nanoparticles Mediated Photodynamic Therapy

Photodynamic therapy (PDT) is able to non-invasively treat and diagnose various cancers and nonmalignant diseases by combining light, oxygen, and photosensitizers (PSs). However, the application of PDT is hindered by poor water solubility and limited light-penetration depth of the currently available photosensitizers (PSs). Water solubility of PSs is crucial for designing pharmaceutical formulation and administration routes. Wavelength of light source at visible range normally has therapeutic depth less than 1 mm. In this review, focus is on the recent research progress of metal-based nanoparticles being applied in PDT. The potential toxicity of these nanoscales and future directions are further discussed.

Effect of PGE2-EPs pathway on primary cultured rat neuron injury caused by aluminum

To observe the characteristic changes of PGE₂-EP_s pathway and divergent functions of PGE₂ receptor subtypes on neuronal injury. The primary cultured rat hippocampus neuron injury model was established via aluminum maltolate (100 μM). The aluminum-overload neurons were treated with the agonists of EP1 (17-phenyl trinor Prostaglandin E2 ethyl amide), EP2 (Butaprost), EP3 (Sulprostone) and EP4 (CAY10598) and antagonists of EP1 (SC-19220), EP2 (AH6809) and EP4 (L-161982) at different concentrations, respectively. The neuronal viability, lactate dehydrogenase leakage rate and PGE2 content were detected by MTT assay, lactate dehydrogenase assay kit and enzyme-linked immunosorbent assay, respectively. The mRNA and protein expressions of mPGES-1 and EPs were determined by RT-PCR and western blot, respectively. The pathomorphology was identified by hematoxylin-eosin staining. In the model group, neuronal viability significantly decreased, while lactate dehydrogenase leakage rate and PGE2 content increased. The mPGES-1, EP1, EP2 and EP4 mRNA expression, and the mPGES-1, EP1 and EP2 protein expression increased, while EP₃ level decreased. EP3 agonist exerted protective function in neuronal viability and lactate dehydrogenase leakage rate, while EP1 agonist, EP2 and EP4 antagonist exerted an opposite effect. In conclusion, aluminum-overload caused an imbalance of PGE₂-EP_1-4 pathway and activation of EP receptor may provide a viable therapeutic target in neuronal injury.

Apo E-Functionalization of Solid Lipid Nanoparticles Enhances Brain Drug Delivery: Uptake Mechanism and Transport Pathways

Several strategies have been implemented to enhance brain drug delivery, and herein solid lipid nanoparticles functionalized with apolipoprotein E were tested in hCMEC/D3 cell monolayers. The mean diameter of 160 nm, negative charge of -12 mV, and their lipophilic characteristics make these nanosystems suitable for brain delivery. Confocal images and flow cytometry data showed a cellular uptake increase of 1.8-fold for SLN-Palmitate-ApoE and 1.9-fold for SLN-DSPE-ApoE when compared with the non-functionalized SLNs. Clathrin-mediated endocytosis was distinguished as the preferential internalization pathway involved in cellular uptake and nanoparticles could cross the blood-brain barrier predominantly by a transcellular pathway. The understanding of the mechanisms involved in the transport of these nanosystems through the blood-brain barrier may potentiate their application on brain drug delivery.

Lactobacillus plantarum CCFM639 Alleviate Trace Element Imbalance-Related Oxidative Stress in Liver and Kidney of Chronic Aluminum Exposure Mice

Aluminum (Al) has various adverse effects on health of humans and animals. The aim of present study was to demonstrate that Lactobacillus plantarum CCFM639 can alleviate the adverse effects on liver and kidney of mice caused by chronic Al exposure. Animals were assigned into control, CCFM639 only, Al only, Al plus CCFM639, and Al plus deferiprone groups. The strain was given by oral gavage for 14 weeks, and Al was introduced via drinking water for the first 8 weeks. Analyses of Al and trace elements levels in feces, blood, and tissues were performed. The biochemical markers (GSH, GPx, SOD, CAT, and MDA) of oxidative stress in livers and kidneys, as well as the levels of ALT, AST, BUN, and CRE in blood, were determined. Our results showed that L. plantarum CCFM639 can significantly reduce Al accumulation in tissues, regulate imbalance of trace elements, and thereby alleviate oxidative stress and pathological changes in hepatic and renal tissues. Therefore, L. plantarum CCFM639 could alleviate Al-induced hepatic and renal injuries, and the possible mechanisms may involve in regulating the imbalance of trace elements.

In vitro toxicity assessment of oral nanocarriers

The fascinating properties of nanomaterials opened new frontiers in medicine. Nanocarriers are useful systems in transporting drugs to site-specific targets. The unique physico-chemical characteristics making nanocarriers promising devices to treat diseases may also be responsible for potential adverse effects. In order to develop functional nano-based drug delivery systems, efficacy and safety should be carefully evaluated. To date, no common testing strategy to address nanomaterial toxicological challenges has been generated. Different cell culture models are currently used to evaluate nanocarrier safety using conventional in vitro assays, but overall they have generated a huge amount of conflicting data. In this review we describe state-of-the-art approaches for in vitro testing of orally administered nanocarriers, highlighting the importance of developing harmonized and validated standard operating procedures. These procedures should be applied in a safe-by-design context with the aim to reduce and/or eliminate the uncertainties and risks associated with nanomedicine development.

Gut: An underestimated target organ for Aluminum

Since World War II, several factors such as an impressive industrial growth, an enhanced environmental bioavailability and intensified food consumption have contributed to a significant amplification of human exposure to aluminum. Aluminum is particularly present in food, beverages, some drugs and airbone dust. In our food, aluminum is superimposed via additives and cooking utensils. Therefore, the tolerable intake of aluminum is exceeded for a significant part of the world population, especially in children who are more vulnerable to toxic effects of pollutants than adults. Faced with this oral aluminum influx, intestinal tract is an essential barrier, especially as 38% of ingested aluminum accumulates at the intestinal mucosa. Although still poorly documented to date, the impact of oral exposure to aluminum in conditions relevant to real human exposure appears to be deleterious for gut homeostasis. Aluminum ingestion affects the regulation of the permeability, the microflora and the immune function of intestine. Nowadays, several arguments are consistent with an involvement of aluminum as an environmental risk factor for inflammatory bowel diseases.

Cellular uptake and transcytosis of lipid-based nanoparticles across the intestinal barrier: Relevance for oral drug delivery

Oral administration is the preferred route for drug delivery and nanosystems represent a promising tool for protection and transport of hardly soluble, chemically unstable and poorly permeable drugs through the intestinal barrier. In the present work, we have studied lipid nanoparticles cellular uptake, internalization pathways and transcytosis routes through Caco-2 cell monolayers. Both lipid nanosystems presented similar size (∼180nm) and surface charge (-30mV). Nanostructured lipid carriers showed a higher cellular uptake and permeability across the barrier, but solid lipid nanoparticles could enter cells faster than the former. The internalization of lipid nanoparticles occurs mainly through a clathrin-mediated endocytosis mechanism, although caveolae-mediated endocytosis is also involved in the uptake. Both lipid nanoparticles were able to cross the intestinal barrier by a preferential transcellular route. This work contributed to a better knowledge of the developed nanosystems for the oral delivery of a wide spectrum of drugs.

Alternating magnetic field-induced hyperthermia increases iron oxide nanoparticle cell association/uptake and flux in blood-brain barrier models

PURPOSE

Superparamagnetic iron oxide nanoparticles (IONPs) are being investigated for brain cancer therapy because alternating magnetic field (AMF) activates them to produce hyperthermia. For central nervous system applications, brain entry of diagnostic and therapeutic agents is usually essential. We hypothesized that AMF-induced hyperthermia significantly increases IONP blood-brain barrier (BBB) association/uptake and flux.

METHODS

Cross-linked nanoassemblies loaded with IONPs (CNA-IONPs) and conventional citrate-coated IONPs (citrate-IONPs) were synthesized and characterized in house. CNA-IONP and citrate-IONP BBB cell association/uptake and flux were studied using two BBB Transwell(®) models (bEnd.3 and MDCKII cells) after conventional and AMF-induced hyperthermia exposure.

RESULTS

AMF-induced hyperthermia for 0.5 h did not alter CNA-IONP size but accelerated citrate-IONP agglomeration. AMF-induced hyperthermia for 0.5 h enhanced CNA-IONP and citrate-IONP BBB cell association/uptake. It also enhanced the flux of CNA-IONPs across the two in vitro BBB models compared to conventional hyperthermia and normothermia, in the absence of cell death. Citrate-IONP flux was not observed under these conditions. AMF-induced hyperthermia also significantly enhanced paracellular pathway flux. The mechanism appears to involve more than the increased temperature surrounding the CNA-IONPs.

CONCLUSIONS

Hyperthermia induced by AMF activation of CNA-IONPs has potential to increase the BBB permeability of therapeutics for the diagnosis and therapy of various brain diseases.

The binding, transport and fate of aluminium in biological cells

Aluminium is the most abundant metal in the Earth's crust and yet, paradoxically, it has no known biological function. Aluminium is biochemically reactive, it is simply that it is not required for any essential process in extant biota. There is evidence neither of element-specific nor evolutionarily conserved aluminium biochemistry. This means that there are no ligands or chaperones which are specific to its transport, there are no transporters or channels to selectively facilitate its passage across membranes, there are no intracellular storage proteins to aid its cellular homeostasis and there are no pathways which evolved to enable the metabolism and excretion of aluminium. Of course, aluminium is found in every compartment of every cell of every organism, from virus through to Man. Herein we have investigated each of the 'silent' pathways and metabolic events which together constitute a form of aluminium homeostasis in biota, identifying and evaluating as far as is possible what is known and, equally importantly, what is unknown about its uptake, transport, storage and excretion.

Human intestinal epithelial cells exhibit a cellular response indicating a potential toxicity upon exposure to hematite nanoparticles

This study examined the effects of different-sized nanoparticles on potential cytotoxicity in intestinal epithelia. Three sizes of hematite nanoparticles were used for the study at a 10 ppm concentration: 17, 53, and, 100 nm. Results indicate that, of the hematite nanoparticles tested, 17 nm was more toxic to the epithelial integrity than 53 or 100 nm. In addition, the epithelial integrity was affected by disruption of epithelial structures such as apical microvilli, and by disruption of the cell-cell junctions leading to reduction in transepithelial electrical resistance measurements (TEER). The drop in TEER was caused by disruption of the adhering junctions not by cell death, as determined by immunocytochemistry, and by using a cell viability assay. Epithelial integrity was also affected at the molecular level as shown by differential expression of genes related to cell junction maintenance, which was assessed by microarray analysis. In conclusion, the 17- and 100-nm hematite nanoparticles caused significant structural changes in the epithelium but not the 53 nm nanoparticles. Also, different-sized hematite nanoparticles each had different effects both at the cellular level and genetic level.

Aluminium-maltolate-induced impairment of learning, memory and hippocampal long-term potentiation in rats

Recently, aluminium (Al) has been proposed to be one of the environmental factors responsible for cause Alzheimer's disease (AD). However, the relationship between Al and AD is controversial. To investigate the effects of subchronic Aluminium-maltolate (Al (mal)(3)) exposure on the behavioral, electrophysiological functions. Forty Sprague-Dawley (SD) rats were randomly distributed into five groups. Over two months, rats in the saline group received daily intraperitoneal (i.p.) injections 0.9% saline, rats in the maltolate group received 7.56 mg/kg maltolate, and rats in the 0.27, 0.54, 1.08 mg/kg Al (mal)(3) groups received i.p. administrations of these three doses, respectively. Neural behavior was assessed in Morris water maze. Long-term potentiation (LTP) in hippocampus was recorded. Al content in the neocortex was determined using a graphite furnace atomic absorption spectrophotometer. Our studies indicate that subchronic Al (mal)(3) exposure significantly impaired spatial learning and memory abilities, suppressed the LTP in the CA1 hippocampal area, and elevated Al levels in cerebral cortex in a dose-dependent fashion. In conclusion, low doses of Al (mal)(3) can still lead to dramatic Al accumulation in the brain, severely impair learning and memory capacities, and hippocampal LTP.

Apoptosis induction by silica nanoparticles mediated through reactive oxygen species in human liver cell line HepG2

Silica nanoparticles are increasingly utilized in various applications including agriculture and medicine. In vivo studies have shown that liver is one of the primary target organ of silica nanoparticles. However, possible mechanisms of hepatotoxicity caused by silica nanoparticles still remain unclear. In this study, we explored the reactive oxygen species (ROS) mediated apoptosis induced by well-characterized 14nm silica nanoparticles in human liver cell line HepG2. Silica nanoparticles (25-200μg/ml) induced a dose-dependent cytotoxicity in HepG2 cells. Silica nanoparticles were also found to induce oxidative stress in dose-dependent manner indicated by induction of ROS and lipid peroxidation and depletion of glutathione (GSH). Quantitative real-time PCR and immunoblotting results showed that both the mRNA and protein expressions of cell cycle checkpoint gene p53 and apoptotic genes (bax and caspase-3) were up-regulated while the anti-apoptotic gene bcl-2 was down-regulated in silica nanoparticles treated cells. Moreover, co-treatment of ROS scavenger vitamin C significantly attenuated the modulation of apoptotic markers along with the preservation of cell viability caused by silica nanoparticles. Our data demonstrated that silica nanoparticles induced apoptosis in human liver cells, which is ROS mediated and regulated through p53, bax/bcl-2 and caspase pathways. This study suggests that toxicity mechanisms of silica nanoparticles should be further investigated at in vivo level.

Metal-based nanoparticles and their toxicity assessment

Nanoparticles (NPs) can potentially cause adverse effects on organ, tissue, cellular, subcellular, and protein levels due to their unusual physicochemical properties (e.g., small size, high surface area to volume ratio, chemical composition, crystallinity, electronic properties, surface structure reactivity and functional groups, inorganic or organic coatings, solubility, shape, and aggregation behavior). Metal NPs, in particular, have received increasing interest due to their widespread medical, consumer, industrial, and military applications. However, as particle size decreases, some metal-based NPs are showing increased toxicity, even if the same material is relatively inert in its bulk form (e.g., Ag, Au, and Cu). NPs also interact with proteins and enzymes within mammalian cells and they can interfere with the antioxidant defense mechanism leading to reactive oxygen species generation, the initiation of an inflammatory response and perturbation and destruction of the mitochondria causing apoptosis or necrosis. As a result, there are many challenges to overcome before we can determine if the benefits outweigh the risks associated with NPs.

Fatty acids increase paracellular absorption of aluminium across Caco-2 cell monolayers

Passive paracellular absorption, regulated by tight junctions (TJs), is the main route for absorption of poorly absorbed hydrophilic substances. Surface active substances, such as fatty acids, may enhance absorption of these substances by affecting the integrity of TJ and increasing the permeability. It has been suggested that aluminium (Al) absorption occurs mainly by the paracellular route. Herein, we investigated if physiologically relevant exposures of fully differentiated Caco-2 cell monolayers to oleic acid and docosahexaenoic acid (DHA), which are fatty acids common in food, increase absorption of Al and the paracellular marker mannitol. In an Al toxicity test, mannitol and Al absorption through Caco-2 cell monolayers were similarly modulated by Al concentrations between 1 and 30mM, suggesting that absorption of the two compounds occurred via the same pathways. Exposure of Caco-2 cell monolayers to non-toxic concentrations of Al (2mM) and (14)C-mannitol in fatty acid emulsions (15 and 30mM oleic acid, 5 and 10mM DHA) caused a decreased transepithelial electrical resistance (TEER). Concomitantly, fractional absorption of Al and mannitol, expressed as percentage of apical Al and mannitol retrieved at the basolateral side, increased with increasing dose of fatty acids. Transmission electron microscopy was applied to assess the effect of oleic acid on the morphology of TJ. It was shown that oleic acid caused a less structured morphology of TJ in Caco-2 cell monolayers. Taken together our findings indicate that fatty acids common in food increase the paracellular intestinal absorption of Al. These findings may influence future risk assessment of human Al exposure.

Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy

The rapid proliferation of many different engineered nanomaterials (defined as materials designed and produced to have structural features with at least one dimension of 100 nanometers or less) presents a dilemma to regulators regarding hazard identification. The International Life Sciences Institute Research Foundation/Risk Science Institute convened an expert working group to develop a screening strategy for the hazard identification of engineered nanomaterials. The working group report presents the elements of a screening strategy rather than a detailed testing protocol. Based on an evaluation of the limited data currently available, the report presents a broad data gathering strategy applicable to this early stage in the development of a risk assessment process for nanomaterials. Oral, dermal, inhalation, and injection routes of exposure are included recognizing that, depending on use patterns, exposure to nanomaterials may occur by any of these routes. The three key elements of the toxicity screening strategy are: Physicochemical Characteristics, In Vitro Assays (cellular and non-cellular), and In Vivo Assays. There is a strong likelihood that biological activity of nanoparticles will depend on physicochemical parameters not routinely considered in toxicity screening studies. Physicochemical properties that may be important in understanding the toxic effects of test materials include particle size and size distribution, agglomeration state, shape, crystal structure, chemical composition, surface area, surface chemistry, surface charge, and porosity. In vitro techniques allow specific biological and mechanistic pathways to be isolated and tested under controlled conditions, in ways that are not feasible in in vivo tests. Tests are suggested for portal-of-entry toxicity for lungs, skin, and the mucosal membranes, and target organ toxicity for endothelium, blood, spleen, liver, nervous system, heart, and kidney. Non-cellular assessment of nanoparticle durability, protein interactions, complement activation, and pro-oxidant activity is also considered. Tier 1 in vivo assays are proposed for pulmonary, oral, skin and injection exposures, and Tier 2 evaluations for pulmonary exposures are also proposed. Tier 1 evaluations include markers of inflammation, oxidant stress, and cell proliferation in portal-of-entry and selected remote organs and tissues. Tier 2 evaluations for pulmonary exposures could include deposition, translocation, and toxicokinetics and biopersistence studies; effects of multiple exposures; potential effects on the reproductive system, placenta, and fetus; alternative animal models; and mechanistic studies.