Contemplating a role for titanium in organisms

Hepatotoxicity of titanium dioxide nanoparticles

The food additive E171 (titanium dioxide, TiO2), is widely used in foods, pharmaceuticals and cosmetics. It is a fine white powder, with at least one third of its particles sized in the nanoparticulate (˂100 nm range, TiO2 NPs). The use of E171 is controversial as its relevant risk assessment has never been satisfactorily accomplished. In vitro and in vivo studies have shown dose-dependent toxicity in various organs including the liver. TiO2 NPs have been shown to induce inflammation, cell death and structural and functional changes within the liver. The toxicity of TiO2 NPs in experimental models varies between organs and according to their physiochemical characteristics and parameters such as dosage and route of administration. Among these factors, ingestion is the most significant exposure route, and the liver is a key target organ. The aim of this review is to highlight the reported adverse effects of orally administered TiO2 NPs on the liver and to discuss the controversial state of its toxicity.

Prenatal exposure to silver is associated with an elevated risk for neural tube defects: a case-control study

Exposure to copper, silver, and titanium has been reported to be associated with a variety of adverse effects on humans, but it is little focused on the fetus. We investigated the associations between prenatal exposure to the three metals (copper, silver, and titanium) and risk for fetal neural tube defects (NTDs). Placental samples from 408 women with pregnancies affected by NTDs and 593 women with normal pregnancies were collected from 2003 to 2016 in Pingding, Xiyang, Shouyang, Taigu, and Zezhou counties of China. Multilevel mixed-effects logistic regression and Bayesian kernel machine regression (BKMR) were used to evaluate the single and joint effects of the metals on NTDs. Silver was associated with an increased risk for NTDs in a dose-response fashion in single-metal logistic regression, with adjusted odds ratios (95% confidence intervals) of 1.78 (1.04-3.06) and 1.92 (1.11-3.32) in the second and third tertiles, respectively, compared to the lowest tertile. BKMR revealed toxic effects of silver on NTDs and the association appeared to be linear. No interaction of silver with any of the other two metals was observed. Besides, silver concentration was positively correlated with maternal certain dietary intakes. Placental high silver concentrations are associated with an elevated risk for NTDs. Maternal diet may be a source of silver exposure.

The elements of life: A biocentric tour of the periodic table

Living systems are built from a small subset of the atomic elements, including the bulk macronutrients (C,H,N,O,P,S) and ions (Mg,K,Na,Ca) together with a small but variable set of trace elements (micronutrients). Here, we provide a global survey of how chemical elements contribute to life. We define five classes of elements: those that are (i) essential for all life, (ii) essential for many organisms in all three domains of life, (iii) essential or beneficial for many organisms in at least one domain, (iv) beneficial to at least some species, and (v) of no known beneficial use. The ability of cells to sustain life when individual elements are absent or limiting relies on complex physiological and evolutionary mechanisms (elemental economy). This survey of elemental use across the tree of life is encapsulated in a web-based, interactive periodic table that summarizes the roles chemical elements in biology and highlights corresponding mechanisms of elemental economy.

The quintessence of metallomics: a harbinger of a different life science based on the periodic table of the bioelements

This year marks the 20th anniversary of the field of metallomics. As a landmark in time, it is an occasion to reflect on the past, present, and future of this integrated field of biometal sciences. A fundamental bias is one reason for having metallomics as a scientific discipline. The focus of biochemistry on the six non-metal chemical elements, collectively known with the acronym SPONCH (sulphur, phosphorus, oxygen, nitrogen, carbon, hydrogen), glosses over the fact that the lower quantities of many other elements have qualities that made them instrumental in the evolution of life and pivotal in numerous life processes. The metallome, alongside the genome, proteome, lipidome, and glycome, should be regarded as a fifth pillar of elemental-vis-à-vis molecular-building blocks in biochemistry. Metallomics as 'global approaches to metals in the biosciences' considers the biological significance of most chemical elements in the periodic table, not only the ones essential for life, but also the non-essential ones that are present in living matter-some at higher concentrations than the essential ones. The non-essential elements are bioactive with either positive or negative effects. Integrating the significance of many more chemical elements into the life sciences requires a transformation in learning and teaching with a focus on elemental biology in addition to molecular biology. It should include the dynamic interactions between the biosphere and the geosphere and how the human footprint is changing the ecology globally and exposing us to many additional chemical elements that become new bioelements.

Interaction of TiO2 nanoparticles with soil: Effect on microbiological and chemical traits

Titanium dioxide (TiO₂) nanoparticles (NPs) are the most widely used nanomaterials and their expanding use raises concerns about their impacts on soil ecosystems and functioning. The present study evaluates the potential impacts of TiO₂ NPs applied at low doses (0, 1.0, 2.5, 5.0, 10.0 and 20.0 mg L^-1) on soil chemical properties including the macro and micronutrient contents, microbial population and enzyme activities in rhizosphere soil of mung bean crop at different time intervals (7, 14, 28 and 56 days). A quantitative RT-PCR study was also performed to study the relative change in the gene expression of ammonia oxidizer and nitrogen fixers upon TiO₂ NP supplementation. An increase in soil nutrient content viz., available N, P, Cu, Fe, Mn, nitrate-N and ammonical-N was observed with NP application except available K and Zn content. The TiO₂ NPs stimulated the growth of soil microflora at low concentrations while an inhibitory effect was recorded at high concentrations. The soil fungi and actinobacteria emerged as the most sensitive groups of soil microbes towards TiO₂ NP exposure exhibiting detrimental impacts on their growth at all concentrations. Similarly, the soil enzyme activities enhanced till TiO₂ NPs (10.0 mg L^-1) which was followed by decrease at higher concentrations. The qRT-PCR study showed that the ammonia oxidizers were more affected by TiO₂ NPs application than nitrogen fixers. These findings suggest that TiO₂ NPs can be used as stimulators of soil nutrients and soil microbial dynamics at low concentrations.

Exploring Titanium(IV) Complexes as Potential Antimicrobial Compounds

Due to the rapid mutation of pathogenic microorganisms, drug-resistant superbugs have evolved. Antimicrobial-resistant germs may share their resistance genes with other germs, making them untreatable. The search for more combative antibiotic compounds has led researchers to explore metal-based strategies centered on perturbing the bioavailability of essential metals in microbes and examining the therapeutic potential of metal complexes. Given the limited knowledge on the application of titanium(IV), in this work, eight Ti(IV) complexes and some of their corresponding ligands were screened by the Community for Open Antimicrobial Drug Discovery for antimicrobial activity. The compounds were selected for evaluation because of their low cytotoxic/antiproliferative behavior against a human non-cancer cell line. At pH 7.4, these compounds vary in terms of their solution stability and ligand exchange lability; therefore, an assessment of their solution behavior provides some insight regarding the importance of the identity of the metal compound to the antimicrobial therapeutic potential. Only one compound, Ti(deferasirox)₂, exhibited promising inhibitory activity against the Gram-positive bacteria methicillin-resistant Staphylococcus aureus and minimal toxicity against human cells. The ability of this compound to undergo transmetalation with labile Fe(III) sources and, as a consequence, inhibit Fe bioavailability and ribonucleotide reductase is evaluated as a possible mechanism for its antibiotic effect.

Titanium for Orthopedic Applications: An Overview of Surface Modification to Improve Biocompatibility and Prevent Bacterial Biofilm Formation

Titanium and its alloys have emerged as excellent candidates for use as orthopedic biomaterials. Nevertheless, there are often complications arising after implantation of orthopedic devices, most notably prosthetic joint infection and aseptic loosening. To ensure that implanted devices remain functional in situ, innovation in surface modification has attracted much attention in the effort to develop orthopedic materials with optimal characteristics at the biomaterial-tissue interface. This review will draw together metallurgy, surface engineering, biofilm microbiology, and biomaterial science. It will serve to appreciate why titanium and its alloys are frequently used orthopedic biomaterials and address some of the challenges facing these biomaterials currently, including the significant problem of device-associated infection. Finally, the authors shall consolidate and evaluate surface modification techniques employed to overcome some of these issues by offering a unique perspective as to the direction in which research is headed from a broad, interdisciplinary point of view.

TiO2 exposure alters transition metal ion quota in Rhodococcus ruber GIN-1

After exposure to micron-sized TiO2 particles, anatase and/or rutile, Rhodococcus ruber GIN-1 accumulates an increased concentration (2.2 ± 0.2 mg kg-1) of mobilized Ti into its biomass with concomitant decreases in cellular biometals Fe, Zn, and possibly Mn, while levels of Cu and Al are unaffected.

Review of the nature of some geophagic materials and their potential health effects on pregnant women: some examples from Africa

The voluntary human consumption of soil known as geophagy is a global practice and deep-rooted in many African cultures. The nature of geophagic material varies widely from the types to the composition. Generally, clay and termite mound soils are the main materials consumed by geophagists. Several studies revealed that gestating women across the world consume more soil than other groups for numerous motives. These motivations are related to medicinal, cultural and nutrients supplementation. Although geophagy in pregnancy (GiP) is a universal dynamic habit, the highest prevalence has been reported in African countries such as Kenya, Ghana, Rwanda, Nigeria, Tanzania, and South Africa. Geophagy can be both beneficial and detrimental. Its health effects depend on the amount and composition of the ingested soils, which is subjective to the geology and soil formation processes. In most cases, the negative health effects concomitant with the practice of geophagy eclipse the positive effects. Therefore, knowledge about the nature of geophagic material and the health effects that might arise from their consumption is important.

Biochemical responses of freshwater mussel Unio tumidus to titanium oxide nanoparticles, Bisphenol A, and their combination

Multiple interactions between different pollutants in the surface waters can cause unpredictable consequences. The aim of the study was to evaluate the combined effect of two widespread xenobiotics, titanium oxide nanoparticles (TiO₂) and bisphenol A (BPA), on freshwater bivalve Unio tumidus. The specimens were exposed for 14 days to TiCl₄ (Ti, 1.25 µM), TiO₂ (1.25 μM), BPA (0.88 nM), or their combination (TiO₂ + BPA). Every type of exposure resulted in a particular oxidative stress response: TiO₂ had antioxidant effect, decreasing the generation of reactive oxygen species (ROS) and phenoloxidase (PhO) activity, and doubling reduced glutathione (GSH) concentration in the digestive gland; Ti caused oxidative changes by increasing levels of ROS, PhO and superoxide dismutase; BPA decreased the GSH level by a factor of two. In the co-exposure treatment, these indices as well as lysosomal membrane stability were not affected. All Ti-containing exposures caused elevated levels of metalated metallothionein (Zn,Cu-MT), its ratio to total metallothionein protein, and lactate/pyruvate ratio. Both BPA-containing exposures decreased caspase-3 activity. All exposures, and particularly co-exposure, up-regulated CYP450-dependent oxidation, lipid peroxidation and lipofuscin accumulation, lysosomal cathepsin D and its efflux, as well as alkali-labile phosphates in gonads and caused DNA instability (except for TiO₂). To summarize, co-exposure to TiO₂ + BPA produced an overlap of certain individual responses but strengthened the damage. Development of water purification technologies using TiO₂ requires further studies of the biological effects of its mixtures. U. tumidus can serve as a sentinel organism in such studies.

From sea squirts to squirrelfish: facultative trace element hyperaccumulation in animals

The hyperaccumulation of trace elements is a widely characterized phenomenon in plants, bacteria, and fungi, but has received little attention in animals. However, there are numerous examples of animals that specifically and facultatively accumulate trace elements in the absence of elevated environmental concentrations. Metal hyperaccumulating animals are usually marine invertebrates, likely owing to environmental (e.g. constant exposure via the water) and physiological (e.g. osmoconforming and reduced integument permeability) factors. However, there are examples of terrestrial animals (insect larvae) and marine vertebrates (e.g. squirrelfish) that accumulate high body and/or tissue metal burdens. This review examines examples of animal hyperaccumulation of the elements arsenic, copper, iron, titanium, vanadium and zinc, describing mechanisms by which accumulation occurs and, where possible, hypothesizing functional roles. Groups such as the ascidians (sea squirts), molluscs (gastropods, bivalves and cephalopods) and polychaete annelids feature prominently as animals with hyperaccumulating capacity. Many of these species are potential model organisms offering insight into fundamental processes underlying metal handling, with relevance to human disease and aquatic metal toxicity, and some offer promise in applied fields such as bioremediation.

Exploring titanium(IV) chemical proximity to iron(III) to elucidate a function for Ti(IV) in the human body

Despite its natural abundance and widespread use as food, paint additive, and in bone implants, no specific biological function of titanium is known in the human body. High concentrations of Ti(IV) could result in cellular toxicity, however, the absence of Ti toxicity in the blood of patients with titanium bone implants indicates the presence of one or more biological mechanisms to mitigate toxicity. Similar to Fe(III), Ti(IV) in blood binds to the iron transport protein serum transferrin (sTf), which gives credence to the possibility of its cellular uptake mechanism by transferrin-directed endocytosis. However, once inside the cell, how sTf bound Ti(IV) is released into the cytoplasm, utilized, or stored remain largely unknown. To explain the molecular mechanisms involved in Ti use in cells we have drawn parallels with those for Fe(III). Based on its chemical similarities with Fe(III), we compare the biological coordination chemistry of Fe(III) and Ti(IV) and hypothesize that Ti(IV) can bind to similar intracellular biomolecules. The comparable ligand affinity profiles suggest that at high Ti(IV) concentrations, Ti(IV) could compete with Fe(III) to bind to biomolecules and would inhibit Fe bioavailability. At the typical Ti concentrations in the body, Ti might exist as a labile pool of Ti(IV) in cells, similar to Fe. Ti could exhibit different types of properties that would determine its cellular functions. We predict some of these functions to mimic those of Fe in the cell and others to be specific to Ti. Bone and cellular speciation and localization studies hint toward various intracellular targets of Ti like phosphoproteins, DNA, ribonucleotide reductase, and ferritin. However, to decipher the exact mechanisms of how Ti might mediate these roles, development of innovative and more sensitive methods are required to track this difficult to trace metal in vivo.

The role of citrate, lactate and transferrin in determining titanium release from surgical devices into human serum

The presence of ionic titanium in the serum of patients with titanium implants is currently unexplained. This is presumed due to corrosion, and yet the serum titanium concentration measured in patients is far greater than that predicted by its solubility. The binding of titanium ion as Ti(IV) to human transferrin (hTF) in serum indicates that Ti(IV) ions interact with human physiology. This is an intriguing finding since there is currently no known role for titanium ions in human physiology. Thus, understanding the factors that determine in vivo titanium ion release is relevant to further understanding this metal's interactions with human biochemistry. The present study sought to determine the extent of titanium ion release of into human serum in vitro, and the role of citrate, lactate and hTF in this process. It was found that, when surgical devices of commercially pure titanium were placed into human serum, citrate and lactate concentrations were the prime determinants of titanium release. Crystallography revealed Ti(IV) bound to hTF in the presence of citrate alone, signalling that citrate can act as an independent ligand for Ti(IV) binding to hTF. Based on these findings, a two-stage process of titanium ion release into human serum that is dependent upon both citrate and hTF is proposed to explain the ongoing presence of titanium ion in human subjects with implanted titanium devices.

Are clinical findings of systemic titanium dispersion following implantation explained by available in vitro evidence? An evidence-based analysis

Although the presence of titanium wear particles released into tissues is known to induce local inflammation following the therapeutic implantation of titanium devices into humans, the role that titanium ions play in adverse tissue responses has received little attention. Support that ongoing titanium ion release occurs is evidenced by the presence of ionic titanium bound to transferrin in blood, and ongoing excretion in the urine of patients with titanium devices. However, as reports documenting the presence of titanium within tissues do not distinguish between particulate and ionic forms due to technical challenges, the degree to which ionic titanium is released into tissues is unknown. To determine the potential for titanium ion release into tissues, this study evaluates available in vitro evidence relating to the release of ionic titanium under physiological conditions. This is a systematic literature review of studies reporting titanium ion release into solutions from titanium devices under conditions replicating the interstitial pH and constituents. Inclusion and exclusion criteria were defined. Of 452 articles identified, titanium ions were reported in nine media relevant to human biology in seventeen studies. Only one study, using human serum replicated both physiological pH and the concentration of constituents while reporting the presence of titanium ions. While there is insufficient information to explain the factors that contribute to the presence of titanium ions in serum of humans implanted with titanium devices, currently available information suggests that areas of future inquiry include the role of transferrin and organic acids.

A ubiquitous metal, difficult to track: towards an understanding of the regulation of titanium(iv) in humans

Despite the ubiquitous nature of titanium(iv) and several examples of its beneficial behavior in different organisms, the metal remains underappreciated in biology. There is little understanding of how the metal might play an important function in the human body. Nonetheless, a new insight is obtained regarding the molecular mechanisms that regulate the blood speciation of the metal to maintain it in a nontoxic and potentially bioavailable form for use in the body. This review surveys the literature on Ti(iv) application in prosthetics and in the development of anticancer therapeutics to gain an insight into soluble Ti(iv) influx in the body and its long-term impact. The limitation in analytical tools makes it difficult to depict the full picture of how Ti(iv) is transported and distributed throughout the body. An improved understanding of Ti function and its interaction with biomolecules will be helpful in developing future technologies for its imaging in the body.

Titanium as a Beneficial Element for Crop Production

Titanium (Ti) is considered a beneficial element for plant growth. Ti applied via roots or leaves at low concentrations has been documented to improve crop performance through stimulating the activity of certain enzymes, enhancing chlorophyll content and photosynthesis, promoting nutrient uptake, strengthening stress tolerance, and improving crop yield and quality. Commercial fertilizers containing Ti, such as Tytanit and Mg-Titanit, have been used as biostimulants for improving crop production; however, mechanisms underlying the beneficial effects still remain unclear. In this article, we propose that the beneficial roles Ti plays in plants lie in its interaction with other nutrient elements primarily iron (Fe). Fe and Ti have synergistic and antagonistic relationships. When plants experience Fe deficiency, Ti helps induce the expression of genes related to Fe acquisition, thereby enhancing Fe uptake and utilization and subsequently improving plant growth. Plants may have proteins that either specifically or nonspecifically bind with Ti. When Ti concentration is high in plants, Ti competes with Fe for ligands or proteins. The competition could be severe, resulting in Ti phytotoxicity. As a result, the beneficial effects of Ti become more pronounced during the time when plants experience low or deficient Fe supply.

Does titanium in ionic form display a tissue-specific distribution?

Most studies have focused on the biodistribution of titanium(IV) oxide as nanoparticles or crystals in organism. But several reports suggested that titanium is released from implant in ionic form. Therefore, gaining insight into toxicokinetics of Ti ions will give valuable information, which may be useful when assessing the health risks of long-term exposure to titanium alloy implants in patients. A micro synchrotron radiation-induced X-ray fluorescence (µ-SRXRF) was utilized to investigate the titanium distribution in the liver, spleen and kidneys of rats following single intravenous or 30-days oral administration of metal (6 mg Ti/b.w.) in ionic form. Titanium was mainly retained in kidneys after both intravenous and oral dosing, and also its compartmentalization in this organ was observed. Titanium in the liver was non-uniformly distributed—metal accumulated in single aggregates, and some of them were also enriched in calcium. Correlation analysis showed that metal did not displace essential elements, and in liver titanium strongly correlated with calcium. Two-dimensional maps of Ti distribution show that the location of the element is characteristic for the route of administration and time of exposure. We demonstrated that µ-SRXRF can provide information on the distribution of titanium in internal structures of whole organs, which helps in enhancing our understanding of the mechanism of ionic titanium accumulation in the body. This is significant due to the popularity of titanium implants and the potential release of metal ions from them to the organism.