Imaging by Elemental and Molecular Mass Spectrometry Reveals the Uptake of an Arsenolipid in the Brain of Drosophila melanogaster

Toxic arsenolipids bioaccumulate in the developing brain of pilot whales

Arsenic-containing hydrocarbons (AsHC), a subclass of arsenolipids (AsL), have been proven to exert neuro- and cytotoxic effects in in-vitro and in-vivo studies and were shown to pass through biological barriers like the blood-brain barrier. However, there has been no connection as to the environmental relevance of these findings, meaning there is no study based on samples from free living animals that are exposed to these compounds. Here, we report the identification of two AsHC as well as 3 arsenosugar phospholipids (AsPL) in the brains of a pod of stranded long-finned pilot whales (Globicephala melas) as well as the absence of arsenobetaine (AsB) which is often found to be a dominant As species in fish. We show data which suggests that there is an age-dependent accumulation of AsL in the brains of the animals. The results show that, in contrast to other organs, total arsenic as well as arsenolipids accumulate in an asymptotic pattern in the brains of the animals. Total As concentrations were found to range from 87 to 260 μg As/kg wet weight and between 0.6 and 27.6 μg As/kg was present in the form of AsPL958 in the brains of stranded pilot whales which was the most dominant lipophilic species present. The asymptotic relationship between total As, as well as AsPL, concentration in the brain and whale age may suggest that the accumulation of these species takes place prior to the full development of the blood-brain barrier in young whales. Finally, comparison between the organs of local squid, a common source of food for pilot whales, highlighted a comparable AsL profile which indicates a likely bioaccumulation pathway through the food chain.

Speciation of arsenic in milk from cows fed seaweed

BACKGROUND

Including seaweed in cattle feed has gained increased interest, but it is important to take into account that the concentration of toxic metals, especially arsenic, is high in seaweed. This study investigated the arsenic species in milk from seaweed-fed cows.

RESULTS

Total arsenic in milk of control diets (9.3 ± 1.0 μg As kg-1, n = 4, dry mass) was significantly higher than seaweed-based diet (high-seaweed diet: 7.8 ± 0.4 μg As kg-1, P < 0.05, n = 4, dry mass; low-seaweed diet: 6.2 ± 1.0 μg As kg-1, P < 0.01, n = 4, dry mass). Arsenic speciation showed that the main species present were arsenobetaine (AB) and arsenate (As(V)) (37% and 24% of the total arsenic, respectively). Trace amounts of dimethylarsinic acid (DMA) and arsenocholine (AC) have also been detected in milk. Apart from arsenate being significantly lower (P < 0.001) in milk from seaweed-fed cows than in milk from the control group, other arsenic species showed no significant differences between groups.

CONCLUSION

The lower total arsenic and arsenate in seaweed diet groups indicates a possible competition of uptake between arsenate and phosphate, and the presence of AC indicates that a reduction of AB occurred in the digestive tract. Feeding a seaweed blend (91% Ascophyllum nodosum and 9% Laminaria digitata) does not raise As-related safety concerns for milk. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Exploring the Effect of Arsenic-Containing Hydrocarbon on the Bidirectional Synaptic Plasticity of the Dorsal Hippocampus

Arsenic-containing hydrocarbons (AsHCs) are common in marine organisms. However, there is little research on their effects on the central nervous system's advanced activities, such as cognition. Bidirectional synaptic plasticity dynamically regulates cognition through the balance of long-term potentiation (LTP) and long-term depression (LTD). However, the effects of AsHCs on bidirectional synaptic plasticity and the underlying molecular mechanisms remain unexplored. This study provides the first evidence that 15 μg As L-1 AsHC 360 enhances bidirectional synaptic plasticity, occurring during the maintenance phase rather than the baseline phase. Further calcium gradient experiments hypothesize that AsHC 360 may enhance bidirectional synaptic plasticity by affecting calcium ion levels. The enhancement of bidirectional synaptic plasticity by 15 μg As L-1 AsHC 360 holds significant implications in improving cognitive function, treating neuro-psychiatric disorders, promoting neural recovery, and enhancing brain adaptability.

Speciation analysis and toxicity evaluation of arsenolipids-an overview focusing on sea food

Arsenic, which can be divided into inorganic and organic arsenic, is a toxic metalloid that has been identified as a human carcinogen. A common source of arsenic exposure in seafood is arsenolipid, which is a complex structure of lipid-soluble organic arsenic compounds. At present, the known arsenolipid species mainly include arsenic-containing fatty acids (AsFAs), arsenic-containing hydrocarbons (AsHCs), arsenic glycophospholipids (AsPLs), and cationic trimethyl fatty alcohols (TMAsFOHs). Furthermore, the toxicity between different species is unique. However, the mechanism underlying arsenolipid toxicity and anabolism remain unclear, as arsenolipids exhibit a complex structure, are present at low quantities, and are difficult to extract and detect. Therefore, the objective of this overview is to summarize the latest research progress on methods to evaluate the toxicity and analyze the main speciation of arsenolipids in seafood. In addition, novel insights are provided to further elucidate the speciation, toxicity, and anabolism of arsenolipids and assess the risks on human health.

Metabolic and genetic derangement: a review of mechanisms involved in arsenic and lead toxicity and genotoxicity

Urbanisation and industrialisation are on the rise all over the world. Environmental contaminants such as potentially toxic elements (PTEs) are directly linked with both phenomena. Two PTEs that raise greatest concern are arsenic (As) and lead (Pb) as soil and drinking water contaminants, whether they are naturally occurring or the consequence of human activities. Both elements are potential carcinogens. This paper reviews the mechanisms by which As and Pb impair metabolic processes and cause genetic damage in humans. Despite efforts to ban or limit their use, due to high persistence both continue to pose a risk to human health, which justifies the need for further toxicological research.

Arsenolipids in raw and cooked seafood products in southwest China: A non-targeted analysis

Arsenolipids are the primary form of arsenic in the fat of marine organisms. Because seafood is a common source of arsenic exposure and some arsenolipids are toxic, studying the abundance and species of arsenolipids in seafood is crucial for health risk assessment. Current arsenolipid research is confined by analytical techniques and limited to raw seafood analysis, despite the fact that most seafood is ingested cooked. Therefore, the aim of this study is to evaluate which seafood contributes to arsenolipid dietary intake and investigate the changes in arsenolipids before and after cooking. In Chongqing, China, popular seafood such as clam, shrimp, oyster, abalone, hairtail, and yellow croaker were collected. The raw and cooked samples prepared from these seafood products were examined using a non-targeted screening approach established for arsenolipids, which coupled high-performance liquid chromatography with data-independent high-resolution quadrupole-time-of-flight electrospray ionization tandem mass spectrometry. Arsenic-containing hydrocarbons (AsHC330, AsHC332, and AsHC360), arsenic-containing fatty acids (AsFA362, AsFA390, AsFA404, AsFA418, and AsFA422), trimethylarsine oxide, and thiolated trimethylarsinic acid were detected. The species of arsenolipids in each type of seafood remained intact after heating in the microwave oven. In cooked samples, the concentrations of AsFA362 and AsFA390 were significantly lower than in raw samples, whereas the concentrations of other arsenolipids were unchanged. Microwave cooking did not result in the thiolation of the detected arsenolipids. The most detected species in raw and cooked samples were AsFA362, AsFA390, and AsFA418. Most arsenolipid species were found in the highest levels in hairtails and yellow croakers. It is the first time that arsenolipids have been found in the oyster, abalone, abalone liver, and yellow croaker. The present study contributes to a better understanding of arsenolipids exposure from seafood, which is useful for assessing the health risks of arsenic.

Arsenolipids reduce butyrate levels and influence human gut microbiota in a donor-dependent way

Arsenolipids are organic arsenic species with variable toxicity. Accurate assessment of the risks derived from arsenic-contaminated seafood intake requires studying the interplay between arsenolipids and the human gut microbiota. This research used the in vitro mucosal simulator of the human intestinal microbial ecosystem (M-SHIME) to assess the effect of defined chemical standards of arsenolipids (AsFA 362 and AsHC 332) on a simulated healthy human gut microbiota (n = 4). Microbial-derived metabolites were quantified by gas chromatography and microbiota structure was characterized by 16S rRNA gene sequencing. A specific reduction in butyrate production (control=5.28 ± 0.3 mM; AsFAs=4.56 ± 0.4 mM; AsHC 332=4.4 ± 0.6 mM, n = 4 donors), concomitant with a reduction in the abundance of Lachnospiraceae UCG-004 group and the Faecalibacterium genus was observed, albeit in a donor-dependent manner. Furthermore, an increase in Escherichia/Shigella, Proteobacteria and Fusobacterium abundance was observed after arsenolipid treatments, depending on individual microbiota background. These alterations in microbial functionality and microbial community structure suggest a detrimental effect of arsenolipids intake towards the commensal gut microbiome, and consequently, on human health.

Facets of ICP-MS and their potential in the medical sciences-Part 1: fundamentals, stand-alone and hyphenated techniques

Since its inception in the early 80s, inductively coupled plasma–mass spectrometry has developed to the method of choice for the analysis of elements in complex biological systems. High sensitivity paired with isotopic selectivity and a vast dynamic range endorsed ICP-MS for the inquiry of metals in the context of biomedical questions. In a stand-alone configuration, it has optimal qualities for the biomonitoring of major, trace and toxicologically relevant elements and may further be employed for the characterisation of disrupted metabolic pathways in the context of diverse pathologies. The on-line coupling to laser ablation (LA) and chromatography expanded the scope and application range of ICP-MS and set benchmarks for accurate and quantitative speciation analysis and element bioimaging. Furthermore, isotopic analysis provided new avenues to reveal an altered metabolism, for the application of tracers and for calibration approaches. In the last two decades, the scope of ICP-MS was further expanded and inspired by the introduction of new instrumentation and methodologies including novel and improved hardware as well as immunochemical methods. These additions caused a paradigm shift for the biomedical application of ICP-MS and its impact in the medical sciences and enabled the analysis of individual cells, their microenvironment, nanomaterials considered for medical applications, analysis of biomolecules and the design of novel bioassays. These new facets are gradually recognised in the medical communities and several clinical trials are underway. Altogether, ICP-MS emerged as an extremely versatile technique with a vast potential to provide novel insights and complementary perspectives and to push the limits in the medical disciplines. This review will introduce the different facets of ICP-MS and will be divided into two parts. The first part will cover instrumental basics, technological advances, and fundamental considerations as well as traditional and current applications of ICP-MS and its hyphenated techniques in the context of biomonitoring, bioimaging and elemental speciation. The second part will build on this fundament and describe more recent directions with an emphasis on nanomedicine, immunochemistry, mass cytometry and novel bioassays.

Gut microbiota metabolize arsenolipids in a donor dependent way

Understanding the interplay between the gut microbiome and arsenolipids can help us manage the potential health risk of consuming seafood, but little is known about the bioconversion fate of arsenolipids in the gastrointestinal tract. We use an in vitro mucosal simulator of the human intestinal microbial ecosystem (M-SHIME) to mimic the digestive tract of four healthy donors during exposure to two arsenolipids (an arsenic fatty acid AsFA 362 or an arsenic hydrocarbon AsHC 332). The metabolites were analyzed by HPLC-mass spectrometry. The human gut bacteria accumulated arsenolipids in a donor-dependent way, with higher retention of AsHC 332. Colonic microbiota partly transformed both arsenolipids to their thioxo analogs, while AsFA 362 was additionally transformed into arsenic-containing fatty esters, arsenic-containing fatty alcohols, and arsenic-containing sterols. There was no significant difference in water-soluble arsenicals between arsenolipid treatments. The study shows that arsenolipids can be quickly biotransformed into several lipid-soluble arsenicals of unknown toxicity, which cannot be excluded when considering potential implications on human health.

Exposure to arsenolipids and inorganic arsenic from marine-sourced dietary supplements

Dietary supplements sourced from marine environments, such as fish oils and seaweed-based supplements, are widely consumed to boost nutrient intakes, including by vulnerable populations such as pregnant women. Like other marine foods, these supplements are also a potential source of exposure to arsenic, including the known toxic species, inorganic arsenic, and the cytotoxic, lipid-soluble arsenic compounds, arsenic hydrocarbons. A study of 32 marine-sourced supplements found higher total arsenic concentrations (>1000 ng g^-1) in supplements made from seaweed, krill and calanus oil, and in fish and fish liver products marketed as "unprocessed". Inorganic arsenic was only detectable in the seaweed samples, and was elevated (8900 ng g^-1) in one product. Arsenic hydrocarbons were not detected in krill oil samples but were present at concentrations from 169 to 2048 ng g^-1 in "unprocessed" fish and fish liver oil, and calanus oil. Survey data from the New Hampshire Birth Cohort Study (NHBCS) found 13.5% of pregnant women (n = 1997) reported taking fish oil supplements; and of those, most did so daily (75.6%, 6 or more times per week). Only a small percentage (9%) of those who reported consuming fish oil used products associated with higher arsenic levels. Higher urinary arsenic concentrations were found among women who consumed fish oil compared with those who did not, and specifically higher arsenobetaine and dimethyl arsenic concentrations. Dietary supplements are becoming common components of modern diets, and some marine-sourced dietary supplements are a source of inorganic arsenic and arsenic hydrocarbons.

The Need to Unravel Arsenolipid Transformations in Humans

The main source of arsenic exposure to humans worldwide is the diet, in particular, drinking water, rice, and seafood. Although arsenic is often considered toxic, it can exist in food as more than 300 chemical species with different toxicities. This diversity makes it difficult for food safety and health authorities to regulate arsenic levels in food, which are currently based on a few arsenic species. Of particular interest are arsenolipids, a type of arsenic species widely found in seafood. Emerging evidence indicates that there are risks associated with human exposure to arsenolipids (e.g., accumulation in breast milk, ability to cross the blood-brain barrier and accumulate in the brain, and potential development of neurodegenerative disorders). Still, more research is needed to fully understand the impact of arsenolipid exposure, which requires establishing interdisciplinary collaborations.

Arsenolipids in salmon are partly converted to thioxo analogs during cooking

BACKGROUND

Arsenic hydrocarbons, major arsenolipids occurring naturally in marine fish, have substantial cytotoxicity leading to human health-related studies of their distribution and abundance in foods. These studies have all investigated fresh foods; because most fish are cooked before being consumed, it is both food- and health-relevant to determine the arsenolipids present in cooked fish.

METHODS

We used HPLC/mass spectrometry to investigate the arsenolipids present in salmon (Salmo salar) before and after cooking by either baking or steaming.

RESULTS

In raw salmon (total As 2.74 mg kg^-1 dry mass, of which 6% was lipid-soluble), major arsenolipids were three arsenic hydrocarbons (oxo-AsHC 332, oxo-AsHC 360, and oxo-AsHC 404, ca 55% of total arsenolipids) and a band of unidentified less-polar arsenolipids (ca 40%), trace amounts of another four arsenic hydrocarbons and two thioxo analogs were also detected. During the cooking process, 28% of the oxo-AsHCs were converted to their thioxo analogs.

CONCLUSION

Our study shows that arsenic hydrocarbons naturally present in fresh fish are partly converted to their thioxo analogs during cooking by either baking or steaming. The greater lipophilicity of the thioxo analogs could alter the mode of toxicity of arsenic hydrocarbons, and hence future food regulations for arsenic should consider the influence of cooking on the precise type of arsenolipid in fish.

LA-ICP-MS and MALDI-MS image registration for correlating nanomaterial biodistributions and their biochemical effects

Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) imaging and matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) are complementary methods that measure distributions of elements and biomolecules in tissue sections. Quantitative correlations of the information provided by these two imaging modalities requires that the datasets be registered in the same coordinate system, allowing for pixel-by-pixel comparisons. We describe here a computational workflow written in Python that accomplishes this registration, even for adjacent tissue sections, with accuracies within ±50 μm. The value of this registration process is demonstrated by correlating images of tissue sections from mice injected with gold nanomaterial drug delivery systems. Quantitative correlations of the nanomaterial delivery vehicle, as detected by LA-ICP-MS imaging, with biochemical changes, as detected by MALDI-MSI, provide deeper insight into how nanomaterial delivery systems influence lipid biochemistry in tissues. Moreover, the registration process allows the more precise images associated with LA-ICP-MS imaging to be leveraged to achieve improved segmentation in MALDI-MS images, resulting in the identification of lipids that are most associated with different sub-organ regions in tissues.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Imaging in Biology

Elemental imaging gives insight into the fundamental chemical makeup of living organisms. Every cell on Earth is comprised of a complex and dynamic mixture of the chemical elements that define structure and function. Many disease states feature a disturbance in elemental homeostasis, and understanding how, and most importantly where, has driven the development of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) as the principal elemental imaging technique for biologists. This review provides an outline of ICP-MS technology, laser ablation cell designs, imaging workflows, and methods of quantification. Detailed examples of imaging applications including analyses of cancers, elemental uptake and accumulation, plant bioimaging, nanomaterials in the environment, and exposure science and neuroscience are presented and discussed. Recent incorporation of immunohistochemical workflows for imaging biomolecules, complementary and multimodal imaging techniques, and image processing methods is also reviewed.

Effect of arsenic-containing hydrocarbon on the long-term potentiation at Schaffer Collateral-CA1 synapses from infantile male rat

Arsenic-containing hydrocarbons (AsHCs) are common constituents of marine organisms and have potential toxicity to human health. This work is to study the effect of AsHCs on long-term potentiation (LTP) for the first time. A multi-electrode array (MEA) system was used to record the field excitatory postsynaptic potential (fEPSP) of CA1 before and after treatment with AsHC 360 in hippocampal slices from infantile male rats. The element content of Na, K, Ca, Mg, Mn, Cu, Zn, and As in the hippocampal slices were analyzed by elemental mass spectrometry after the neurophysiological experiment. The results showed that low AsHC 360 (1.5 μg As L^-1) had no effect on the LTP, moderate AsHC 360 (3.75-15 μg As L^-1) enhanced the LTP, and high AsHC 360 (45-150 μg As L^-1) inhibited the LTP. The enhancement of the LTP by promoting Ca²⁺ influx was proved by a Ca²⁺ gradient experiment. The inhibition of the LTP was likely due to damage of synaptic cell membrane integrity. This study on the neurotoxicity of AsHCs showed that high concentrations have a strong toxic effect on the LTP in hippocampus slices of the infantile male rat, which may lead to a negative effect on the development, learning, and memory.

Discovery and Identification of Arsenolipids Using a Precursor-Finder Strategy and Data-Independent Mass Spectrometry

Arsenolipids are a class of lipid-soluble arsenic species. They are present in seafoods and show high potentials of cytotoxicity and neurotoxicity. Hindered by traditional low-throughput analytical techniques, the characterization of arsenolipids is far from complete. Here, we report on a sensitive and high-throughput screening method for arsenolipids in krill oil, tuna fillets, hairtail heads, and kelp. We demonstrate the detection and identification of 23 arsenolipids, including novel arsenic-containing fatty acids (AsFAs), hydroxylated AsFAs, arsenic-containing hydrocarbons (AsHCs), hydroxylated AsHCs, thiolated trimethylarsinic acids, and arsenic-containing lysophosphatidylcholines not previously reported. The new method incorporated precursor ion scan (PIS) into data-independent acquisition. High-performance liquid chromatography (HPLC) electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-qToF-MS) was used to perform the sequential window acquisition of all theoretical spectra (SWATH). Comprehensive HPLC-MS and MS/MS data were further processed using a fragment-guided chromatographic computational program Precursorfinder developed here. Precursorfinder achieved efficient peak-picking, retention time comparison, hierarchical clustering, and wavelet coherence calculations to assemble fragment features with their target precursors. The identification of arsenolipids was supported by coeluting the HPLC-MS peaks detected with the characteristic fragments of arsenolipids. Method validation using available arsenic standards and the successful identification of previously unknown arsenolipids in seafood samples demonstrated the applicability of the method for environmental research.

Toxicological assessment of arsenic-containing phosphatidylcholines in HepG2 cells

Arsenolipids include a wide range of organic arsenic species that occur naturally in seafood and thereby contribute to human arsenic exposure. Recently arsenic-containing phosphatidylcholines (AsPCs) were identified in caviar, fish, and algae. In this first toxicological assessment of AsPCs, we investigated the stability of both the oxo- and thioxo-form of an AsPC under experimental conditions, and analyzed cell viability, indicators of genotoxicity and biotransformation in human liver cancer cells (HepG2). Precise toxicity data could not be obtained owing to the low solubility in the cell culture medium of the thioxo-form, and the ease of hydrolysis of the oxo-form, and to a lesser degree the thioxo-form. Hydrolysis resulted amongst others in the respective constituent arsenic-containing fatty acid (AsFA). Incubation of the cells with oxo-AsPC resulted in a toxicity similar to that determined for the hydrolysis product oxo-AsFA alone, and there were no indices for genotoxicity. Furthermore, the oxo-AsPC was readily taken up by the cells resulting in high cellular arsenic concentrations (50 μM incubation: 1112 ± 146 μM As cellular), whereas the thioxo-AsPC was substantially less bioavailable (50 μM incubation: 293 ± 115 μM As cellular). Speciation analysis revealed biotransformation of the AsPCs to a series of AsFAs in the culture medium, and, in the case of the oxo-AsPC, to as yet unidentified arsenic species in cell pellets. The results reveal the difficulty of toxicity studies of AsPCs in vitro, indicate that their toxicity might be largely governed by their arsenic fatty acid content and suggest a multifaceted human metabolism of food derived complex arsenolipids.

Cellular toxicological characterization of a thioxolated arsenic-containing hydrocarbon

Arsenolipids, especially arsenic-containing hydrocarbons (AsHC), are an emerging class of seafood originating contaminants. Here we toxicologically characterize a recently identified oxo-AsHC 332 metabolite, thioxo-AsHC 348 in cultured human liver (HepG2) cells. Compared to results of previous studies of the parent compound oxo-AsHC 332, thioxo-AsHC 348 substantially affected cell viability in the same concentration range but exerted about 10-fold lower cellular bioavailability. Similar to oxo-AsHC 332, thioxo-AsHC 348 did not substantially induce oxidative stress nor DNA damage. Moreover, in contrast to oxo-AsHC 332 mitochondria seem not to be a primary subcellular toxicity target for thioxo-AsHC 348. This study indicates that thioxo-AsHC 348 is at least as toxic as its parent compound oxo-AsHC 332 but very likely acts via a different mode of toxic action, which still needs to be identified.

Transport of arsenolipids to the milk of a nursing mother after consuming salmon fish

OBJECTIVE

We address two questions relevant to infants' exposure to potentially toxic arsenolipids, namely, are the arsenolipids naturally present in fish transported intact to a mother's milk, and what is the efficiency of this transport.

METHODS

We investigated the transport of arsenolipids and other arsenic species present in fish to mother's milk by analyzing the milk of a single nursing mother at 15 sampling times over a 3-day period after she had consumed a meal of salmon. Total arsenic values were obtained by elemental mass spectrometry, and arsenic species were measured by HPLC coupled to both elemental and molecular mass spectrometry.

RESULTS

Total arsenic increased from background levels (0.1 μg As kg-1) to a peak value of 1.72 μg As kg-1 eight hours after the fish meal. The pattern for arsenolipids was similar to that of total arsenic, increasing from undetectable background levels (< 0.01 μg As kg-1) to a peak after eight hours of 0.45 μg As kg-1. Most of the remaining total arsenic in the milk was accounted for by arsenobetaine. The major arsenolipids in the salmon were arsenic hydrocarbons (AsHCs; 55 % of total arsenolipids), and these compounds were also the dominant arsenolipids in the milk where they contributed over 90 % of the total arsenolipids.

CONCLUSIONS

Our study has shown that ca 2-3 % of arsenic hydrocarbons, natural constituents of fish, can be directly transferred unchanged to the milk of a nursing mother. In view of the potential neurotoxicity of AsHCs, the effects of these compounds on the brain developmental stage of infants need to be investigated.

Organoarsenicals in Seafood: Occurrence, Dietary Exposure, Toxicity, and Risk Assessment Considerations - A Review

Diet, especially seafood, is the main source of arsenic exposure for humans. The total arsenic content of a diet offers inadequate information for assessment of the toxicological consequences of arsenic intake, which has impeded progress in the establishment of regulatory limits for arsenic in food. Toxicity assessments are mainly based on inorganic arsenic, a well-characterized carcinogen, and arsenobetaine, the main organoarsenical in seafood. Scarcity of toxicity data for organoarsenicals, and the predominance of arsenobetaine as an organic arsenic species in seafood, has led to the assumption of their nontoxicity. Recent toxicokinetic studies show that some organoarsenicals are bioaccessible and cytotoxic with demonstrated toxicities like that of pernicious trivalent inorganic arsenic, underpinning the need for speciation analysis. The need to investigate and compare the bioavailability, metabolic transformation, and elimination from the body of organoarsenicals to the well-established physiological consequences of inorganic arsenic and arsenobetaine exposure is apparent. This review provides an overview of the occurrence and assessment of human exposure to arsenic toxicity associated with the consumption of seafood.

Mass Spectrometry Imaging of atherosclerosis-affine Gadofluorine following Magnetic Resonance Imaging

Molecular imaging of atherosclerosis by Magnetic Resonance Imaging (MRI) has been impaired by a lack of validation of the specific substrate responsible for the molecular imaging signal. We therefore aimed to investigate the additive value of mass spectrometry imaging (MSI) of atherosclerosis-affine Gadofluorine P for molecular MRI of atherosclerotic plaques. Atherosclerotic Ldlr^−/− mice were investigated by high-field MRI (7 T) at different time points following injection of atherosclerosis-affine Gadofluorine P as well as at different stages of atherosclerosis formation (4, 8, 16 and 20 weeks of HFD). At each imaging time point mice were immediately sacrificed after imaging and aortas were excised for mass spectrometry imaging: Matrix Assisted Laser Desorption Ionization (MALDI) Imaging and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) imaging. Mass spectrometry imaging allowed to visualize the localization and measure the concentration of the MR imaging probe Gadofluorine P in plaque tissue ex vivo with high spatial resolution and thus adds novel and more target specific information to molecular MR imaging of atherosclerosis.

Toxicity of three types of arsenolipids: species-specific effects inCaenorhabditis elegans

AsHCs and AsTAG are highly bioavailable toC. elegans., AsHCs are metabolized byC. elegans., AsHCs but not AsTAG and AsFA affect survival and development inC. elegans.

Dual Mass Spectrometric Tissue Imaging of Nanocarrier Distributions and Their Biochemical Effects

Nanomaterial-based drug delivery vehicles are able to deliver therapeutics in a controlled, targeted manner. Currently, however, there are limited analytical methods that can detect both nanomaterial distributions and their biochemical effects concurrently. In this study, we demonstrate that matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) and laser ablation inductively coupled plasma mass spectrometry imaging (LA-ICP-MSI) can be used together to obtain nanomaterial distributions and biochemical consequences. These studies employ nanoparticle-stabilized capsules (NPSCs) loaded with siRNA as a testbed. MALDI-MSI experiments on spleen tissues from intravenously injected mice indicate that NPSCs loaded with anti-TNF-α siRNA cause changes to the lipid composition in white pulp regions of the spleen, as anticipated, based on pathways known to be affected by TNF-α, whereas NPSCs loaded with scrambled siRNA do not cause the predicted changes. Interestingly, LA-ICP-MSI experiments reveal that the NPSCs primarily localize in the red pulp, suggesting that the observed changes in lipid composition are due to diffusive rather than localized effects on TNF-α production. Such information is only accessible by combining data from the two modalities, which we accomplish by using the heme signals from MALDI-MSI and iron signals from LA-ICP-MSI to overlay the images. Several unexpected changes in lipid composition also occur in regions where the NPSCs are found, suggesting that the NPSCs themselves can influence tissue biochemistry as well.

Mass spectrometry imaging to detect lipid biomarkers and disease signatures in cancer

BACKGROUND

Current methods to identify, classify, and predict tumor behavior mostly rely on histology, immunohistochemistry, and molecular determinants. However, better predictive markers are required for tumor diagnosis and evaluation. Due, in part, to recent technological advancements, metabolomics and lipid biomarkers have become a promising area in cancer research. Therefore, there is a necessity for novel and complementary techniques to identify and visualize these molecular markers within tumors and surrounding tissue.

RECENT FINDINGS

Since its introduction, mass spectrometry imaging (MSI) has proven to be a powerful tool for mapping analytes in biological tissues. By adding the label-free specificity of mass spectrometry to the detailed spatial information of traditional histology, hundreds of lipids can be imaged simultaneously within a tumor. MSI provides highly detailed lipid maps for comparing intra-tumor, tumor margin, and healthy regions to identify biomarkers, patterns of disease, and potential therapeutic targets. In this manuscript, recent advancement in sample preparation and MSI technologies are discussed with special emphasis on cancer lipid research to identify tumor biomarkers.

CONCLUSION

MSI offers a unique approach for biomolecular characterization of tumor tissues and provides valuable complementary information to histology for lipid biomarker discovery and tumor classification in clinical and research cancer applications.

Arsenolipids are not uniformly distributed within two brown macroalgal species Saccharina latissima and Alaria esculenta

Brown macroalgae Saccharina latissima (30-40 individuals) and Alaria esculenta (15-20 individuals) were collected from natural populations in winter in Iceland. The algal thalli were sectioned into different parts (e.g. holdfast, stipe, old frond, young frond and sori-containing frond sections) that differed in age and biological function. The work elucidated that arsenic (As) was not uniformly distributed within the two brown macroalgal species, with lower levels of total As were found in the stipe/midrib compared to other thallus parts. The arsenosugars mirrored the total arsenic in the seaweed mainly due to AsSugSO3 being the most abundant As species. However, arsenic speciation using parallel HPLC-ICP-MS/ESI-MS elucidated that the arsenic-containing lipids (AsL) had a different distribution where the arsenosugarphospholipids (AsPL) differed by approximately a factor of 4 between the sections containing the lowest and highest concentrations of AsPLs. When placing the sections in order of metabolic activity and an estimate of tissue age, there appeared to be a relationship between the activity and AsPLs, with lower levels of AsPLs in oldest parts. This is the first time such a relationship has been shown for AsLs. Hence, by applying sophisticated analytical techniques, it was possible to gain a deeper understanding of arsenolipids in seaweed.

Complementary Molecular and Elemental Mass-Spectrometric Imaging of Human Brain Tumors Resected by Fluorescence-Guided Surgery

Fluorescence-guided surgery (FGS) has been established as a powerful technique for glioblastoma resection. After oral application of the prodrug 5-aminolevulinic acid (5-ALA), protoporphyrin IX (PpIX) is formed as an intermediate of the heme-biosynthesis cascade and accumulates within the tumor. By intraoperative fluorescence microscopy, the specific PpIX fluorescence can be used to differentiate the tumor from healthy brain tissue. To investigate possible limitations of fluorescence diagnosis, the complementary use of molecular and elemental mass-spectrometry imaging (MSI) is presented. Matrix-assisted laser-desorption-ionization mass spectrometry (MALDI-MS) is used to examine the distribution of PpIX and heme b in human brain tumors. MALDI-MS/MS imaging is performed to validate MS data and improve the signal-to-noise ratio (S/N). Comparing the imaging results with histological evaluation, increased PpIX accumulation in areas of high tumor-cell density is observed. Heme b accumulation are only found in areas of blood vessels and hemorrhage, confirming the hampered transformation from PpIX to heme b in glioblastoma tissue. Investigation of non-neoplastic brain tissue and glioblastoma resected without external 5-ALA administration as control samples with true-negative fluorescence verified the absence of PpIX accumulation. Analysis of necrotic tumor tissue and gliosarcoma, one rare type of glioma appearing nonfluorescent during FGS, as case examples with false-negative-fluorescence diagnosis, revealed the absence of significant amounts of PpIX, indicating an impairment of PpIX formation. Molecular analysis is complemented by quantitative laser ablation-inductively coupled plasma (LA-ICP) MSI correlating heme b and Fe distribution. Mathematical pixel-by-pixel correlation of molecular and elemental data revealed a positive correlation with heteroscedasticity for the spatially resolved heme b signal intensities and Fe concentrations.

Arsenic-containing hydrocarbons disrupt a model in vitro blood-cerebrospinal fluid barrier

Lipid-soluble arsenicals, so-called arsenolipids, have gained a lot of attention in the last few years because of their presence in many seafoods and reports showing substantial cytotoxicity emanating from arsenic-containing hydrocarbons (AsHCs), a prominent subgroup of the arsenolipids. More recent in vivo and in vitro studies indicate that some arsenolipids might have adverse effects on brain health. In the present study, we focused on the effects of selected arsenolipids and three representative metabolites on the blood-cerebrospinal fluid barrier (B-CSF-B), a brain-regulating interface. For this purpose, we incubated an in vitro model of the B-CSF-B composed of porcine choroid plexus epithelial cells (PCPECs) with three AsHCs, two arsenic-containing fatty acids (AsFAs) and three representative arsenolipid metabolites (dimethylarsinic acid, thio/oxo-dimethylpropanoic acid) to examine their cytotoxic potential and impact on barrier integrity. The toxic arsenic species arsenite was also tested in this way and served as a reference substance. While AsFAs and the metabolites showed no cytotoxic effects in the conducted assays, AsHCs showed a strong cytotoxicity, being up to 1.5-fold more cytotoxic than arsenite. Analysis of the in vitro B-CSF-B integrity showed a concentration-dependent disruption of the barrier within 72 h. The correlation with the decreased plasma membrane surface area (measured as capacitance) indicates cytotoxic effects. These findings suggest exposure to elevated levels of certain arsenolipids may have detrimental consequences for the central nervous system.

Brimstone chemistry under laser light assists mass spectrometric detection and imaging the distribution of arsenic in minerals

Singly charged As2n+1 ion clusters (n = 2-11) were generated from elemental arsenic by negative-ion laser-ablation mass spectrometry. The overall abundance of the gaseous As ions generated upon laser irradiation was enhanced nearly a hundred times when As-bearing samples were admixed with sulfur. However, sulfur does not act purely as an inert matrix: irradiating arsenic-sulfur mixtures revealed a novel pathway to generate and detect a series of [AsSn]- clusters (n = 2-6). Intriguingly, the spectra recorded from As2O3, NaAsO2, Na3AsO4, cacodylic acid and 3-amino-4-hydroxyphenylarsonic acid together with sulfur as the matrix were remarkably similar to that acquired from an elemental arsenic and sulfur mixture. This result indicated that arsenic sulfide cluster-ions are generated directly from arsenic compounds by a hitherto unknown pathway. The mechanism of elemental sulfur extracting chemically bound arsenic from compounds and forming [AsSn]- clusters is enigmatic; however, this discovery has a practical value as a general detection method for arsenic compounds. For example, the method was employed for the detection of As in its minerals, and for the imaging of arsenic distribution in minerals such as domeykite. LDI-MS data recorded from a latent image imprinted on a piece of paper from a flat mineral surface, and wetting the paper with a solution of sulfur, enabled the localization of arsenic in the mineral. The distribution of As was visualized as false-color images by extracting from acquired data the relative intensities of m/z 139 (AsS2-) and m/z 171 (AsS3-) ions.

Arsenic-containing hydrocarbons: effects on gene expression, epigenetics, and biotransformation in HepG2 cells

Arsenic-containing hydrocarbons (AsHCs), a subgroup of arsenolipids found in fish and algae, elicit substantial toxic effects in various human cell lines and have a considerable impact on cellular energy levels. The underlying mode of action, however, is still unknown. The present study analyzes the effects of two AsHCs (AsHC 332 and AsHC 360) on the expression of 44 genes covering DNA repair, stress response, cell death, autophagy, and epigenetics via RT-qPCR in human liver (HepG2) cells. Both AsHCs affected the gene expression, but to different extents. After treatment with AsHC 360, flap structure-specific endonuclease 1 (FEN1) as well as xeroderma pigmentosum group A complementing protein (XPA) and (cytosine-5)-methyltransferase 3A (DNMT3A) showed time- and concentration-dependent alterations in gene expression, thereby indicating an impact on genomic stability. In the subsequent analysis of epigenetic markers, within 72 h, neither AsHC 332 nor AsHC 360 showed an impact on the global DNA methylation level, whereas incubation with AsHC 360 increased the global DNA hydroxymethylation level. Analysis of cell extracts and cell media by HPLC-mass spectrometry revealed that both AsHCs were considerably biotransformed. The identified metabolites include not only the respective thioxo-analogs of the two AsHCs, but also several arsenic-containing fatty acids and fatty alcohols, contributing to our knowledge of biotransformation mechanisms of arsenolipids.

Mono-acyl arsenosugar phospholipids in the edible brown alga Kombu (Saccharina japonica)

Twenty one arsenolipids, including eight new compounds (AsSugPL 692, AsSugPL 706, AsSugPL 720, AsSugPL 734, AsSugPL 742, AsSugPL 746, AsSugPL 748, and AsSugPL 776) were identified in the edible brown alga Kombu, Saccharina japonica, by means of HPLC coupled with elemental and molecular mass spectrometry. The hitherto undescribed compounds are all mono-acyl arsenosugar phospholipids, differing from previously reported natural arsenic-containing phospholipids by containing only one fatty acid on the glycerol group. Collectively, this new group of mono-acyl compounds constituted about 30% of total lipid arsenic; other significant groups were the di-acyl arsenosugar phospholipids (50%) and arsenic hydrocarbons (20%). The origin and relevance of the mono-acyl arsenosugar phospholipids in Kombu, a commercial seafood product, is briefly discussed.

Effects of arsenolipids on in vitro blood-brain barrier model

Arsenic-containing hydrocarbons (AsHCs), a subgroup of arsenolipids (AsLs) occurring in fish and edible algae, possess a substantial neurotoxic potential in fully differentiated human brain cells. Previous in vivo studies indicating that AsHCs cross the blood-brain barrier of the fruit fly Drosophila melanogaster raised the question whether AsLs could also cross the vertebrate blood-brain barrier (BBB). In the present study, we investigated the impact of several representatives of AsLs (AsHC 332, AsHC 360, AsHC 444, and two arsenic-containing fatty acids, AsFA 362 and AsFA 388) as well as of their metabolites (thio/oxo-dimethylpropionic acid, dimethylarsinic acid) on porcine brain capillary endothelial cells (PBCECs, in vitro model for the blood-brain barrier). AsHCs exerted the strongest cytotoxic effects of all investigated arsenicals as they were up to fivefold more potent than the toxic reference species arsenite (iAs^III). In our in vitro BBB-model, we observed a slight transfer of AsHC 332 across the BBB after 6 h at concentrations that do not affect the barrier integrity. Furthermore, incubation with AsHCs for 72 h led to a disruption of the barrier at sub-cytotoxic concentrations. The subsequent immunocytochemical staining of three tight junction proteins revealed a significant impact on the cell membrane. Because AsHCs enhance the permeability of the in vitro blood-brain barrier, a similar behavior in an in vivo system cannot be excluded. Consequently, AsHCs might facilitate the transfer of accompanying foodborne toxicants into the brain.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

Human exposure to organic arsenic species from seafood

Seafood, including finfish, shellfish, and seaweed, is the largest contributor to arsenic (As) exposure in many human populations. In contrast to the predominance of inorganic As in water and many terrestrial foods, As in marine-derived foods is present primarily in the form of organic compounds. To date, human exposure and toxicological assessments have focused on inorganic As, while organic As has generally been considered to be non-toxic. However, the high concentrations of organic As in seafood, as well as the often complex As speciation, can lead to complications in assessing As exposure from diet. In this report, we evaluate the presence and distribution of organic As species in seafood, and combined with consumption data, address the current capabilities and needs for determining human exposure to these compounds. The analytical approaches and shortcomings for assessing these compounds are reviewed, with a focus on the best practices for characterization and quantitation. Metabolic pathways and toxicology of two important classes of organic arsenicals, arsenolipids and arsenosugars, are examined, as well as individual variability in absorption of these compounds. Although determining health outcomes or assessing a need for regulatory policies for organic As exposure is premature, the extensive consumption of seafood globally, along with the preliminary toxicological profiles of these compounds and their confounding effect on assessing exposure to inorganic As, suggests further investigations and process-level studies on organic As are needed to fill the current gaps in knowledge.

Toxicity of two classes of arsenolipids and their water-soluble metabolites in human differentiated neurons

Arsenolipids are lipid-soluble organoarsenic compounds, mainly occurring in marine organisms, with arsenic-containing hydrocarbons (AsHCs) and arsenic-containing fatty acids (AsFAs) representing two major subgroups. Recently, toxicity studies of several arsenolipids showed a high cytotoxic potential of those arsenolipids in human liver and bladder cells. Furthermore, feeding studies with Drosophila melanogaster indicated an accumulation of arsenolipids in the fruit fly's brain. In this study, the neurotoxic potential of three AsHCs, two AsFAs and three metabolites (dimethylarsinic acid, thio/oxo-dimethylarsenopropanoic acid) was investigated in comparison to the toxic reference arsenite (iAs^III) in fully differentiated human brain cells (LUHMES cells). Thereby, in the case of AsHCs both the cell number and cell viability were reduced in a low micromolar concentration range comparable to iAs^III, while AsFAs and the applied metabolites were less toxic. Mechanistic studies revealed that AsHCs reduced the mitochondrial membrane potential, whereas neither iAs^III nor AsFAs had an impact. Furthermore, neurotoxic mechanisms were investigated by examining the neuronal network. Here, AsHCs massively disturbed the neuronal network and induced apoptotic effects, while iAs^III and AsFAs showed comparatively lesser effects. Taking into account the substantial in vitro neurotoxic potential of the AsHCs and the fact that they could transfer across the physiological barriers of the brain, a neurotoxic potential in vivo for the AsHCs cannot be excluded and needs to be urgently characterized.