[Show abstract][Hide abstract] ABSTRACT: Along with the expanding use of engineered metal oxide nanomaterials (MONMs), there is a growing concern over their unintentional adverse toxicological effects on human health and the environment upon release and exposure. It is inevitable that biota will be exposed to nanomaterials, through intentional administration or inadvertent contact under such circumstances. Therefore, a thorough investigation of the potential nanotoxicity of MONMs at the nano–bio–eco interface is urgently needed. In general, nanomaterials interact with their surrounding environments, biotic and abiotic, immediately upon introduction into the environment. The behavior and fate of MONMs are influenced by the dynamics of the environment. Thus, understanding the interactions at the nano–bio–eco interface is necessary for selecting and designing MONMs with minimum adverse impacts. Despite the limitations of currently available techniques, careful characterization of nanomaterials and the choosing of methodologies that promote further risk assessment promise more reliable and accurate data output. Conventional toxicological analysis techniques lack the power to handle the large datasets generated from in vitro/in vivo observations. This paper provides a comprehensive review of the recent experimental and theoretical studies on the toxicity of MONMs mediated by two-way or three-way interactions. In the Perspectives, we also call for more open collaborations between industry, academia, and research labs to facilitate nanotoxicological studies focused specifically on interactions at the nano–bio–eco interface, leading to safe and effective nanotechnology for commercial, environmental, and medicinal use.
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloids (PAs) widely distribute in plants and can cause hepatic sinusoidal obstruction syndrome (HSOS), which typically presents as a primary sinusoidal endothelial cell damage. It is well-recognized that after ingestion, PAs undergo hepatic cytochromes P450 (CYPs)-mediated metabolic activation to generate dehydropyrrolizidine alkaloids (DHPAs), which are hydrolyzed to dehydroretronecine (DHR). DHPAs and DHR are reactive metabolites having same core pyrrole moiety, and can bind proteins to form pyrrole-protein adducts, which are believed as the primary cause for PA-induced HSOS. However, to date, the direct evidences supporting the toxicity of DHPAs and DHR in the liver, in particular in the sinusoidal endothelial cells, are lacking. Using human hepatic sinusoidal endothelial cells (HSEC) and HepG2 (representing hepatic parenchymal cells), cells that lack CYPs activity, this study determined the direct cytotoxicity of dehydromonocrotaline, a representative DHPA, and DHR, but no cytotoxicity of the intact PA (monocrotaline) in both cell lines, confirming that reactive metabolites mediate PA intoxication. Comparing with HepG2, HSEC had significantly lower basal glutathione (GSH) level, and was significantly more susceptible to the reactive metabolites with severer GSH depletion and pyrrole-protein adducts formation. The toxic potency of two reactive metabolites was also compared. DHPA was more reactive than DHR, leading to severer toxicity. In conclusion, our results unambiguously provided the first direct evidence for the critical role of DHPA and DHR in the reactive metabolites-mediated PA-induced hepatotoxicity, which occurs predominantly in HSEC due to severe GSH depletion and the significant formation of pyrrole-protein adducts in HSEC.
[Show abstract][Hide abstract] ABSTRACT: Although enzyme-like nanomaterials have been extensively investigated over the past decade, most research has focused on the peroxidase-like, catalase-like, or SOD-like activity of these nanomaterials. Identifying nanomaterials having oxidase-like activities has received less attention. In this study, we demonstrate that platinum nanoparticles (Pt NPs) exhibit catechol oxidase-like activity, oxidizing polyphenols into the corresponding o-quinones. Four unique approaches are employed to demonstrate the catechol oxidase-like activity exerted by Pt NPs. First, UV-vis spectroscopy is used to monitor the oxidation of polyphenols catalyzed by Pt NPs. Second, the oxidized products of polyphenols are identified by ultrahigh-performance liquid chromatography (UHPLC) separation followed by high-resolution mass spectrometry (HRMS) identification. Third, electron spin resonance (ESR) oximetry techniques are used to confirm the O2 consumption during the oxidation reaction. Fourth, the intermediate products of semiquinone radicals formed during the oxidation of polyphenols are determined by ESR using spin stabilization. These results indicate Pt NPs possess catechol oxidase-like activity. Because polyphenols and related bioactive substances have been explored as potent antioxidants that could be useful for the prevention of cancer and cardiovascular diseases, and Pt NPs have been widely used in the chemical industry and medical science, it is essential to understand the potential effects of Pt NPs for altering or influencing the antioxidant activity of polyphenols.
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloids (PAs) are hepatotoxic, genotoxic, and carcinogenic in experimental animals. Because of their widespread distribution in the world, PA-containing plants are probably the most common poisonous plants affecting livestock, wildlife, and humans. Upon metabolism, PAs generate reactive dehydro-PAs and other pyrrolic metabolites that lead to toxicity. Dehydro-PAs are known to react with glutathione (GSH) to form 7-GSH-(+/−)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (7-GS-DHP) in vivo and in vitro and 7,9-diGS-DHP in vitro. To date, the phototoxicity of GS-DHP adducts has not been well studied. In this study, we synthesized 7-GS-DHP, a tentatively assigned 9-GS-DHP, and two enantiomeric 7,9-diGS-DHP adducts by reaction of dehydromonocrotaline with GSH. The two 7,9-diGS-DHPs were separated by high performance liquid chromatography (HPLC) and their structures were characterized by 1H nuclear magnetic resonance (NMR) and COSY NMR spectral analysis. Photoirradiation of 7-GS-DHP, 9-GS-DHP, and the two 7,9-diGS-DHPs as well as dehydromonocrotaline, dehydroheliotrine, and the 7-R enantiomer of DHP (DHR), by UVA light at 0 J/cm2, 14 J/cm2, and 35 J/cm2 in the presence of a lipid, methyl linoleate, all resulted in lipid peroxidation in a light dose-responsive manner. The levels of lipid peroxidation induced by the two isomeric 7,9-diGS-DHPs were significantly higher than that by 7-GS-DHP and 9-GS-DHP. When 7,9-diGS-DHP was irradiated in the presence of sodium azide (NaN3), the level of lipid peroxidation decreased; lipid peroxidation was enhanced when methanol was replaced by deuterated methanol. These results suggest that singlet oxygen is a product induced by the irradiation of 7,9-diGS-DHP. When irradiated in the presence of superoxide dismutase (SOD), the level of lipid peroxidation decreased, indicating that lipid peroxidation is also mediated by superoxide. These results indicate that lipid peroxidation is mediated by reactive oxygen species (ROS). These results suggest that 7,9-diGS-DHPs are phototoxic, generating lipid peroxidation mediated by ROS.
Journal of Food and Drug Analysis 07/2015; 19. DOI:10.1016/j.jfda.2015.06.001 · 0.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Etheno-DNA adducts are generated by interaction of cellular DNA with exogenous environmental carcinogens and end-products of lipid peroxidation. It has been determined that 1,N(6)-etheno-2'-deoxyadenosine (εdA) and 3,N(4)-etheno-2'-deoxycytidine (εdC) adducts formed in human white blood cells can be used to serve as biomarkers of genetic damage mediated by oxidative stress. In this study we developed an ultrasensitive UPLC-MS-MS method used to detect and quantify εdA and εdC adducts in human white blood cells. The percent recoveries of εdA and εdC adducts were found to be 88.9% ± 2.8 and 95.7% ± 3.7, respectively. The detection limits were ˜1.45 fmol for εdA and ˜1.27 fmol for εdC in 20 μg of human white blood cell DNA samples, both εdA and εdC adducts could be detected using only ˜ 5 μg of DNA per sample. For validation of the method, 34 human blood cell DNA samples were assayed and the results revealed a significant difference (P<0.01) between levels (fmol/µg DNA) of 0.82 ± 0.83 (SD) (range 0.15-3.11) for εdA, 3.28 ± 3.15 (SD) (range 0.05-9.6) for εdC in benzene-exposed workers; and 0.04 ± 0.08 (SD) (range 0.0-0.27) for εdA and 0.77 ± 1.02 (SD) (range 0.10-4.11) for εdC in non-benzene-exposed workers. Our method shows a high sensitivity and specificity when applied to small amounts of human white blood cell DNA samples, background levels of ɛdA and ɛdC could be reproducibly detected. The ultrasensitive and simple detection method is thus suitable for applications in human biomonitoring and molecular epidemiology studies.
Free Radical Research 05/2015; 49(9):1-24. DOI:10.3109/10715762.2015.1006213 · 2.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloid (PA)-containing plants are the most common poisonous plants affecting livestock, wildlife, and humans. PAs require metabolic activation to form pyrrolic metabolites to exert cytotoxicity and tumorigenicity. We previously determined that metabolism of tumorigenic PAs produced four DNA adducts, designated as DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4, that are responsible for liver tumor initiation. 7-Glutathione-(±)-6,7-dihydro-1-hydroxymethyl-5H-pyrrolizine (7-GSH-DHP) is a PA metabolite formed in vivo and in vitro, and 7,9-di-GSH-DHP is formed in vitro. Both are considered as detoxified metabolites. In this study, we determined that reaction of 7-GSH-DHP with 2'-deoxyguanosine (dG) in water formed DHP-dG-3 and DHP-dG-4 adducts. Similarly, reaction of 7-GSH-DHP with 2'-deoxyadenosine (dA) generated DHP-dA-3 and DHP-dA-4 adducts. Besides, DHP, a reactive metabolite, was also generated. Furthermore, reaction of 7-GSH-DHP with calf thymus DNA in aqueous solution at 37 ◦C for 4, 8, 16, 24, 48, or 72 h, respectively followed by enzymatic hydrolysis all yielded DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4 adducts. Under our current experimental condition, DHP-dA-3 and DHP-dA-4 adducts were formed in a trace amount from reaction of 7,9-di-GSH-DHP with dA. No DHP-dG or DHP-dA adducts were detected from reaction of 7,9-di-GSH-DHP with dG. This study represents the first report that 7-GSH-DHP adduct can be a potential reactive metabolite of PAs leading to DNA adduct formation.
Chemical Research in Toxicology 03/2015; 28(4). DOI:10.1021/tx500417q · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloid-containing plants are widespread in the world and probably the most common poisonous plants affecting livestock, wildlife, and humans. Pyrrolizidine alkaloids require metabolic activation to form dehydropyrrolizidine alkaloids that bind to cellular proteins and DNA leading to hepatotoxicity, genotoxicity, and tumorigenicity. At present, it is not clear how dehydropyrrolizidine alkaloids bind to cellular amino acids and proteins to induced toxicity. We previously reported that reaction of dehydromonocrotaline with valine generated four highly unstable 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived valine (DHP-valine) adducts that upon reaction with phenyl isothiocyanate (PITC) formed four DHP-valine-PITC adduct isomers. In this study, we report the absolute configuration and stability of DHP-valine and DHP-valine-PITC adducts, and the mechanism of interconversion between DHP-valine-PITC adducts.
Journal of Food and Drug Analysis 02/2015; 23(2). DOI:10.1016/j.jfda.2015.01.004 · 0.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nearly 50% of naturally-occurring pyrrolizidine alkaloids (PAs) are hepatotoxic, and the majority of hepatotoxic PAs are retronecine-type PAs (RET-PAs). However, quantitative measurement of PAs in herbs/foodstuffs is often difficult because most of reference PAs are unavailable. In this study, a rapid, selective, and sensitive UHPLC-QTOF–MS method was developed for the estimation of RET-PAs in herbs without requiring corresponding standards. This method is based on our previously established characteristic and diagnostic mass fragmentation patterns and the use of retrorsine for calibration. The use of a single RET-PA (i.e. retrorsine) for construction of calibration was based on high similarities with no significant differences demonstrated by the calibration curves constructed by peak areas of extract ion chromatograms of fragment ion at m/z 120.0813 or 138.0919 versus concentrations of five representative RET-PAs. The developed method was successfully applied to measure a total content of toxic RET-PAs of diversified structures in fifteen potential PA-containing herbs.
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloids, produced by a large number of poisonous plants with wide global distribution, are associated with genotoxicity, tumorigenicity, and hepatotoxicity in animals and humans. Mammalian metabolism converts pyrrolizidine alkaloids to reactive pyrrolic metabolites (dehydropyrrolizidine alkaloids) that form covalent protein and DNA adducts. Although a mechanistic understanding is currently unclear, pyrrolizidine alkaloids can cause secondary (hepatogenous) photosensitization and induce skin cancer. In this study, the phototoxicity of monocrotaline, riddelliine, dehydromonocrotaline, dehydroriddelliine, and dehydroretronecine (DHR) in human HaCaT keratinocytes under ultraviolet A (UVA) irradiation was determined. UVA irradiation of HaCaT cells treated with dehydromonocrotaline, dehydroriddelline, and DHR resulted in increased release of lactate dehydrogenase and enhanced photocytotoxicity proportional to the UVA doses. UVA-induced photochemical DNA damage also increased proportionally with dehydromonocrotaline and dehydroriddelline. UVA treatment potentiated the formation of 8-hydroxy-2'-deoxyguanosine DNA adducts induced by dehydromonocrotaline in HaCaT skin keratinocytes. Using electron spin resistance trapping, we found that UVA irradiation of dehydromonocrotaline and dehydroriddelliine generates reactive oxygen species (ROS), including hydroxyl radical, singlet oxygen, and superoxide, and electron transfer reactions, indicating that cytotoxicity and genotoxicity of these compounds could be mediated by ROS. Our results suggest that dehydropyrrolizidine alkaloids formed or delivered to the skin cause pyrrolizidine alkaloid-induced secondary photosensitization and possible skin cancer.
Journal of Environmental Science and Health Part C Environmental Carcinogenesis & Ecotoxicology Reviews 10/2014; 32(4):362-84. DOI:10.1080/10590501.2014.969980 · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloid-containing plants are probably the most common poisonous plants affecting livestock, wildlife, and humans. Pyrrolizidine alkaloids exert toxicity through metabolism to dehydropyrrolizidine alkaloids that bind to cellular protein and DNA, leading to hepatotoxicity, genotoxicity, and tumorigenicity. To date, it is not clear how dehydropyrrolizidine alkaloids bind to cellular constituents, including amino acids and proteins, resulting in toxicity. Metabolism of carcinogenic monocrotaline, riddelliine, and heliotrine produces dehydromonocrotaline, dehyroriddelliine, and dehydroheliotrine, respectively, as primary reactive metabolites. In this study, we report that reaction of dehydromonocrotaline with valine generated four highly unstable 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived valine (DHP-valine) adducts. For structural elucidation, DHP-valine adducts were derivatized with phenyl isothiocyanate (PITC) to DHP-valine-PITC products. After HPLC separation, their structures were characterized by mass spectrometry, UV-visible spectrophotometry, (1)H NMR, and (1)H-(1)H COSY NMR spectral analysis. Two DHP-valine-PITC adducts, designated as DHP-valine-PITC-1 and DHP-valine-PITC-3, had the amino group of valine linked to the C7 position of the necine base, and the other two DHP-valine-PITC products, DHP-valine-PITC-2 and DHP-valine-PITC-4, linked to the C9 position of the necine base. DHP-valine-PITC-1 was interconvertible with DHP-valine-PITC-3, and DHP-valine-PITC-2 was interconvertible with DHP-valine-PITC-4. Reaction of dehydroriddelliine and dehydroheliotrine with valine provided similar results. However, reaction of valine and dehydroretronecine (DHR) under similar experimental conditions did not produce DHP-valine adducts. Reaction of dehydromonocrotaline with rat hemoglobin followed by derivatization with PITC also generated the same four DHP-valine-PITC adducts. This represents the first full structural elucidation of protein conjugated pyrrolic adducts formed from reaction of dehydropyrrolizidine alkaloids with an amino acid (valine). In addition, it was found that DHP-valine-2 and DHP-valine-4, with the valine amino group linked at the C7 position of the necine base, can lose the valine moiety to form DHP.
Chemical Research in Toxicology 09/2014; 27(10). DOI:10.1021/tx5002139 · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A 2-year cancer bioassay in rodents with a preparation of Aloe vera whole leaf extract administered in drinking water showed clear evidence of carcinogenic activity. To provide insight into the identity and mechanisms associated with mutagenic components of the Aloe vera extracts, we used the mouse lymphoma assay to evaluate the mutagenicity of Aloe vera whole leaf extract (WLE) and Aloe vera decolorized whole leaf extract (WLD). The WLD extract was obtained by subjecting WLE to activated carbon-adsorption. HPLC analysis indicated that the decolorization process removed many components from the WLE extract, including anthraquinones. Both WLE and WLD extracts showed cytotoxic and mutagenic effects in mouse lymphoma cells but at different concentration ranges, and WLD induced about 3-fold higher levels of intracellular reactive oxygen species than WLE. Molecular analysis of mutant colonies from cells treated with WLE and WLD revealed that the primary type of damage from both treatments was largely due to chromosome mutations (deletions and/or mitotic recombination). The fact that the samples were mutagenic at different concentrations suggests that while some mutagenic components of WLE were removed by activated carbon filtration, components with pro-oxidant activity and mutagenic activity remained. The results demonstrate the utility of the mouse lymphoma assay as a tool to characterize the mutagenic activity of fractionated complex botanical mixtures to identify bioactive components.
[Show abstract][Hide abstract] ABSTRACT: Pyrrolizidine alkaloids (PAs) are natural toxins widely distributed in plants. The toxic potencies of different PAs vary significantly. PAs are mono- or di-esters of necine acids with a necine base. Based on the necine bases, PAs are classified into three types: retronecine-type, otonecine-type and platynecine-type. Hepatotoxic PAs contain an unsaturated necine base. PAs exert hepatotoxicity through metabolic activation by hepatic cytochromes P450s (CYPs) to generate reactive intermediates which form pyrrole-protein adducts. These adducts provide a mechanism-based biomarker to assess PA toxicity. In the present study, metabolic activation of twelve PAs from three structural types was investigated firstly in mice to demonstrate significant variations in hepatic metabolic activation of different PAs. Subsequently, the structural and enzymatic factors affecting metabolic activation of these PAs were further investigated by using human liver microsomes and recombinant human CYPs. Pyrrole-protein adducts were detected in the liver and blood of mice and the in vitro systems treated with toxic retronecine-type and otonecine-type PAs having unsaturated necine bases but not with a platynecine-type PA containing a saturated necine base. Retronecine-type PAs produced more pyrrole-protein adducts than otonecine-type PAs with similar necine acids, demonstrating the structure of necine base affected PA toxic potency. Among retronecine-type PAs, open-ring di-esters generated the highest amount of pyrrole-protein adducts, followed by macrocyclic di-esters, while mono-esters produced the least. Only CYP3A4 and CYP3A5 activated otonecine-type PAs, while all ten CYPs studied showed the ability to activate retronecine-type PAs. Moreover, the contribution of major CYPs involved also varied significantly among retronecine-type PAs. In conclusion, our findings provide a scientific basis for predicting the toxicities of individual PAs in biological systems based on PA structural features and on the pattern of expression and the selectivity of the CYP isoforms present.
Chemical Research in Toxicology 05/2014; 27(6). DOI:10.1021/tx500071q · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Due to possessing an extremely small size and a large surface area per unit of volume, nanomaterials have specific characteristic physical, chemical, photochemical, and biological properties that are very useful in many new applications. Nanoparticles' catalytic activity and intrinsic ability in generating or scavenging reactive oxygen species in general can be used to mimic the catalytic activity of natural enzymes. Many nanoparticles with enzyme-like activities have been found, potentially capable of being applied for commercial uses, such as in biosensors, pharmaceutical processes, and the food industry. To date, a variety of nanoparticles, especially those formed from noble metals, have been determined to possess oxidase-like, peroxidase-like, catalase-like, and/or superoxide dismutase-like activity. The ability of nanoparticles to mimic enzymatic activity, especially peroxidase mimics, can be used in a variety of applications, such as detection of glucose in biological samples and waste water treatment. To study the enzyme-like activity of nanoparticles, the electron spin resonance method represents a critically important and convenient analytical approach for zero-time detection of the reactive substrates and products as well as for mechanism determination.
Journal of Environmental Science and Health Part C Environmental Carcinogenesis & Ecotoxicology Reviews 04/2014; 32(2):186-211. DOI:10.1080/10590501.2014.907462 · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanotechnology is a rapidly developing field in the 21(st) century, and the commercial use of nanomaterials for novel applications is increasing exponentially. To date, the scientific basis for the cytotoxicity and genotoxicity of most manufactured nanomaterials are not understood. The mechanisms underlying the toxicity of nanomaterials have recently been studied intensively. An important mechanism of nanotoxicity is the generation of reactive oxygen species (ROS). Overproduction of ROS can induce oxidative stress, resulting in cells failing to maintain normal physiological redox-regulated functions. This in turn leads to DNA damage, unregulated cell signaling, change in cell motility, cytotoxicity, apoptosis, and cancer initiation. There are critical determinants that can affect the generation of ROS. These critical determinants, discussed briefly here, include: size, shape, particle surface, surface positive charges, surface-containing groups, particle dissolution, metal ion release from nanometals and nanometal oxides, UV light activation, aggregation, mode of interaction with cells, inflammation, and pH of the medium.
Journal of Food and Drug Analysis 03/2014; 22(1):64-75. DOI:10.1016/j.jfda.2014.01.005 · 0.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cancer is the second leading cause of death in the USA according to the American Cancer Society. In the past 5 years, "theranostic nanomedicine", for both therapeutics and imaging, has shown to be "the right drug for the right patient at the right moment" to manage deadly cancers. This review article presents an overview of recent developments, mainly from the authors' laboratories, along with potential medical applications for theranostic nanomedicine including basic concepts and critical properties. Finally, we outline the future research direction and possible challenges for theranostic nanomedicine research.
Journal of Food and Drug Analysis 03/2014; 22(1):3-17. DOI:10.1016/j.jfda.2014.01.001 · 0.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plants are used by humans in daily life in many different ways, including as food, herbal medicines, and cosmetics. Unfortunately, many natural plants and their chemical constituents are photocytotoxic and photogenotoxic, and these phototoxic phytochemicals are widely present in many different plant families. To date, information concerning the phototoxicity and photogenotoxicity of many plants and their chemical constituents is limited. In this review, we discuss phototoxic plants and their major phototoxic constituents; routes of human exposure; phototoxicity of these plants and their constituents; general mechanisms of phototoxicity of plants and phototoxic components; and several representative phototoxic plants and their photoactive chemical constituents.
Journal of Environmental Science and Health Part C Environmental Carcinogenesis & Ecotoxicology Reviews 09/2013; 31(3):213-55. DOI:10.1080/10590501.2013.824206 · 3.56 Impact Factor