Induction of oxidative stress by humic acid through increasing intracellular iron: a possible mechanism leading to atherothrombotic vascular disorder in blackfoot disease

Cigarette Smoke Particle-Induced Lung Injury and Iron Homeostasis

It is proposed that the mechanistic basis for non-neoplastic lung injury with cigarette smoking is a disruption of iron homeostasis in cells after exposure to cigarette smoke particle (CSP). Following the complexation and sequestration of intracellular iron by CSP, the host response (eg, inflammation, mucus production, and fibrosis) attempts to reverse a functional metal deficiency. Clinical manifestations of this response can present as respiratory bronchiolitis, desquamative interstitial pneumonitis, pulmonary Langerhans’ cell histiocytosis, asthma, pulmonary hypertension, chronic bronchitis, and pulmonary fibrosis. If the response is unsuccessful, the functional deficiency of iron progresses to irreversible cell death evident in emphysema and bronchiectasis. The subsequent clinical and pathological presentation is a continuum of lung injuries, which overlap and coexist with one another. Designating these non-neoplastic lung injuries after smoking as distinct disease processes fails to recognize shared relationships to each other and ultimately to CSP, as well as the common mechanistic pathway (ie, disruption of iron homeostasis).

Impact of humate substances and Bacillus subtilis PB6 on thyroid activity and histomorphometry, iron profile and blood haematology of quail

The purpose of this study was to assess the effects of dietary humate substances (HS) and CloSTAT (Bacillus subtilis PB6) on the thyroid activity and histology, iron profile, blood haematology and performance of growing Japanese quail. A total of 216 unsexed 7-day-old quail chicks were randomly assigned to six groups. The first group was fed a basal diet (BD) without any additives (control); the 2nd group received BD plus 0.05% CloSTAT, the 3rd and 4th groups were given BD plus 0.4% and 0.8% HS, respectively; and the 5th and 6th groups were administered BD plus CloSTAT + 0.4% HS and BD plus CloSTAT + 0.8% HS, respectively. The results showed that the growth performance was improved with the addition of CloSTAT alone or in combination with 0.4% HS compared with the control. Haematological parameters, iron level and transferrin saturation % were significantly (p < 0.001) increased by feeding HS compared with the control group. Serum thyroxin and triiodothyronine levels were significantly (p = 0.001) increased by adding CloSTAT relative to the control. Supplementation of 0.8% HS caused deterioration in histomorphometry parameters of the thyroid gland, but these parameters were improved in response to CloSTAT compared with the control. In conclusion, dietary B. subtilis PB6 as CloSTAT or CloSTAT + 0.4% HS supplementation may be efficacious in enhancing the growth performance and boosting the thyroid activity of growing Japanese quail. Moreover, the addition of 0.4% or 0.8% HS to quail diets boosted their iron profile and haematological parameters.

Ozone Reacts With Carbon Black to Produce a Fulvic Acid-Like Substance and Increase an Inflammatory Effect

Exposure to ambient ozone has been associated with increased human mortality. Ozone exposure can introduce oxygen-containing functional groups in particulate matter (PM) effecting a greater capacity of the particle for metal complexation and inflammatory effect. We tested the postulate that (1) a fulvic acid-like substance can be produced through a reaction of a carbonaceous particle with high concentrations of ozone and (2) such a fulvic acid-like substance included in the PM can initiate inflammatory effects following exposure of respiratory epithelial (BEAS-2B) cells and an animal model (male Wistar Kyoto rats). Carbon black (CB) was exposed for 72 hours to either filtered air (CB-Air) or approximately 100 ppm ozone (CB-O₃). Carbon black exposure to high levels of ozone produced water-soluble, fluorescent organic material. Iron import by BEAS-2B cells at 4 and 24 hours was not induced by incubations with CB-Air but was increased following coexposures of CB-O₃ with ferric ammonium citrate. In contrast to CB-Air, exposure of BEAS-2B cells and rats to CB-O₃ for 24 hours increased expression of pro-inflammatory cytokines and lung injury, respectively. It is concluded that inflammatory effects of carbonaceous particles on cells can potentially result from (1) an inclusion of a fulvic acid-like substance after reaction with ozone and (2) changes in iron homeostasis following such exposure.

A Fulvic Acid-like Substance Participates in the Pro-inflammatory Effects of Cigarette Smoke and Wood Smoke Particles

We tested the postulates that (1) a fulvic acid (FA)-like substance is included in cigarette smoke and wood smoke particles (WSP) and (2) cell exposure to this substance results in a disruption of iron homeostasis, associated with a deficiency of the metal and an inflammatory response. The fluorescence excitation-emission matrix spectra of the water-soluble components of cigarette smoke condensate and WSP (Cig-WS and Wood-WS) approximated those for the standard reference materials, Suwanee River and Nordic fulvic acids (SRFA and NFA). Fourier transform infrared spectra for the FA fraction of cigarette smoke and WSP (Cig-FA and Wood-FA), SRFA, and NFA also revealed significant similarities (O-H bond in alcohols, phenols, and carboxylates, C═O in ketones, aldehydes, and carboxylates, and a significant carboxylate content). After exposure to Cig-WS and Wood-WS and the FA standards, iron was imported by respiratory epithelial cells, reflecting a functional iron deficiency. The release of pro-inflammatory mediators interleukin (IL)-8 and IL-6 by respiratory epithelial cells also increased following exposures to Cig-WS, Wood-WS, SRFA, and NFA. Co-exposure of the respiratory epithelial cells with iron decreased supernatant concentrations of the ILs relative to exposures to Cig-WS, Wood-WS, SRFA, and NFA alone. It is concluded that (1) a FA-like substance is included in cigarette smoke and WSP and (2) respiratory epithelial cell exposure to this substance results in a disruption of iron homeostasis associated with both a cell deficiency of the metal and an inflammatory response.

The role of humic acids on gemfibrozil toxicity to zebrafish embryos

Climate change is expected to alter the dynamics of water masses, with consequent changes in water quality parameters such as dissolved organic carbon (DOC) concentration. DOC levels play a critical role in the fate of organic chemicals, influencing their bioavailability and toxicity to aquatic organisms. This study aimed to evaluate the effects of DOC, particularly humic acids (HA), in the toxicity of gemfibrozil (GEM) - a human pharmaceutical frequently detected in surface waters. Lethal and sublethal effects (genotoxic, biochemical and behavioural alterations) were evaluated in zebrafish embryos exposed to several concentrations of GEM and three HA levels, in a full factorial design. HA significantly increased GEM LC₅₀ values, mainly in the first 72 h of exposure, showing a protective effect. At sublethal levels, however, such protection was not observed since HA per se elicited adverse effects. At a biochemical level, individual exposure to HA (20 mg/L) elicited significant decreases in cholinesterase and glutathione S-transferase activities. Regarding behaviour, effects of individual exposure to HA appear to surpass the GEM effects, reducing the total distance moved by larvae. Both GEM and HA significantly increased DNA damage. Hence, this study demonstrated that abiotic factors, namely HA, should be considered in the assessment of pharmaceuticals toxicity. Moreover, it showed that lethality may not be enough to characterize combined effects since different patterns of response may occur at different levels of biological organization. Testing sublethal relevant endpoints is thus recommended to achieve a robust risk assessment in realistic scenarios.

The toxicology of air pollution predicts its epidemiology

The epidemiologic investigation has successively delineated associations of air pollution exposure with non-malignant and malignant lung disease, cardiovascular disease, cerebrovascular disease, pregnancy outcomes, perinatal effects and other extra-pulmonary disease including diabetes. Defining these relationships between air pollution exposure and human health closely parallels results of an earlier epidemiologic investigation into cigarette smoking and environmental tobacco smoke (ETS), two other particle-related exposures. Humic-like substances (HULIS) have been identified as a chemical component common to cigarette smoke and air pollution particles. Toxicology studies provide evidence that a disruption of iron homeostasis with sequestration of host metal by HULIS is a fundamental mechanistic pathway through which biological effects are initiated by cigarette smoke and air pollution particles. As a result of a common chemical component and a shared mechanistic pathway, it should be possible to extrapolate from the epidemiology of cigarette smoking and ETS to predict associations of air pollution exposure with human disease, which are currently unrecognized. Accordingly, it is anticipated that the forthcoming epidemiologic investigation will demonstrate relationships of air pollution with COPD causation, peripheral vascular disease, hypertension, renal disease, digestive disease, loss of bone mass/risk of fractures, dental disease, eye disease, fertility problems, and extrapulmonary malignancies.

Human lung injury following exposure to humic substances and humic-like substances

Among the myriad particles the human respiratory tract is exposed to, a significant number are distinctive in that they include humic substances (HS) and humic-like substances (HULIS) as organic components. HS are heterogeneous, amorphous, organic materials which are ubiquitous occurring in all terrestrial and aqueous environments. HULIS are a complex class of organic, macromolecular compounds initially extracted from atmospheric aerosol particles which share some features with HS including an aromatic, polyacidic nature. As a result of having a variety of oxygen-containing functional groups, both HS and HULIS complex metal cations, especially iron. Following particle uptake by cells resident in the lung, host iron will be sequestered by HS- and HULIS-containing particles initiating pathways of inflammation and subsequent fibrosis. It is proposed that (1) human exposures to HS and HULIS of respirable size (<10 µm diameter) are associated with inflammatory and fibrotic lung disease and (2) following retention of particles which include HS and HULIS, the mechanism of cell and tissue injury involves complexation of host iron. Human inflammatory and fibrotic lung injuries following HS and HULIS exposures may include coal workers' pneumoconiosis, sarcoidosis, and idiopathic pulmonary fibrosis as well as diseases associated with cigarette smoking and exposures to emission and ambient air pollution particles.

Neuroprotective effect of humic Acid on focal cerebral ischemia injury: an experimental study in rats

Stroke is still a major cause of death and permanent neurological disability. As humic acids are well-known antioxidant molecules, the purpose of this study was to investigate the potential neuroprotective effects of humic acid in a focal cerebral ischemia model. Twenty-four rats were divided equally into three groups. A middle cerebral artery occlusion model was performed in this study where control (group II) and humic acid (group III) were administered intraperitoneally following an ischemic experimental procedure. Group I was evaluated as sham. Malondialdehyde (MDA), superoxide dismutase (SOD), and nuclear respiratory factor-1 (NRF-1) levels were analyzed biochemically on the right side of the ischemic cerebral hemisphere, while ischemic histopathological studies were completed on the left side to investigate the antioxidant status. Biochemical results showed that SOD and NRF-1 levels were significantly increased in the humic acid group (III) compared with the control group (II) while MDA levels were significantly decreased. On histopathological examination, cerebral edema, vacuolization, degeneration, and destruction of neural elements were decreased in the humic acid group (III) compared with the control group (II). Cerebral ischemia was attenuated by humic acid administration. These observations indicate that humic acid may have potential as a therapeutic agent in cerebral ischemia by preventing oxidative stress.

Humic Acid Increases Amyloid β-Induced Cytotoxicity by Induction of ER Stress in Human SK-N-MC Neuronal Cells

Humic acid (HA) is a possible etiological factor associated with for several vascular diseases. It is known that vascular risk factors can directly increase the susceptibility to Alzheimer’s disease (AD), which is a neurodegenerative disorder due to accumulation of amyloid β (Aβ) peptide in the brain. However, the role that HA contributes to Aβ-induced cytotoxicity has not been demonstrated. In the present study, we demonstrate that HA exhibits a synergistic effect enhancing Aβ-induced cytotoxicity in cultured human SK-N-MC neuronal cells. Furthermore, this deterioration was mediated through the activation of endoplasmic reticulum (ER) stress by stimulating PERK and eIF2α phosphorylation. We also observed HA and Aβ-induced cytotoxicity is associated with mitochondrial dysfunction caused by down-regulation of the Sirt1/PGC1α pathway, while in contrast, treating the cells with the ER stress inhibitor Salubrinal, or over-expression of Sirt1 significantly reduced loss of cell viability by HA and Aβ. Our findings suggest a new mechanism by which HA can deteriorate Aβ-induced cytotoxicity through modulation of ER stress, which may provide significant insights into the pathogenesis of AD co-occurring with vascular injury.

Mechanism of the toxicity induced by natural humic acid on human vascular endothelial cells

Humic acid (HA), a group of high-molecular weight organic compounds characterized by an ability to bind heavy metals, is normally found in natural water. Although the impairment of vascular endothelial cells in the presence of humic substances has been reported to be involved in some diseases, the mechanisms responsible for this involvement remain unclear. In this study, we examined the cytotoxicity of HA obtained from peatland in Central Kalimantan, Indonesia, to human vascular endothelial cells, as well as the mechanisms behind these effects. It was found that 50 mg/L HA showed cytotoxicity, which we considered to be mediated by apoptosis through the mitochondrial pathway because of an increase in the expression of caspases 6 and 9 in response to HA administration. In addition, this cytotoxicity was enhanced when cells in this experimental system were exposed to oxidative stress, while it was decreased by the addition of vitamin C. Thus, we conclude that the apoptosis induced by HA depends upon oxidative stress. Furthermore, an iron chelator, DFO, showed a tendency to decrease HA-induced cytotoxicity, suggesting that iron may potentially mediate HA-induced oxidative stress. In conclusion, long-term consumption of HA-rich water obtained from our study area may cause damage to endothelial cells and subsequent chronic health problems.

Humic acid enhances cigarette smoke-induced lung emphysema in mice and IL-8 release of human monocytes

Tobacco smoke is the main factor in the etiology of lung emphysema. Generally prolonged, substantial exposure is required to develop the disease. Humic acid is a major component of cigarette smoke that accumulates in smokers' lungs over time and induces tissue damage.

OBJECTIVES

To investigate whether humic acid pre-loading potentiates the development of cigarette smoke-induced lung emphysema in mice and increases IL-8 release by human monocytes.

METHODS

C57BL/6J mice received humic acid or aqueous vehicle by tracheal installation on day 0 and day 7. From day 21 to day 84, the mice were exposed to cigarette smoke or clean air for 5 days/week. Twenty-four hours after the last exposure we determined leukocytes in lung lavage, heart hypertrophy and alveolar wall destruction. Human monocytes were incubated with cigarette smoke extract (CSE), humic acid or the combination overnight.

RESULTS

Humic acid nor cigarette smoke caused alveolar wall destruction within two months. Interestingly, the combination did induce lung emphysema. Humic acid, cigarette smoke or the combination did not change leukocyte types and numbers in lung lavage fluid, but the combination caused peribronchiolar and perivascular lymphocyte infiltration. Humic acid treatment resulted in a high proportion of alveolar macrophages heavily loaded with intracellular granula. Humic acid also induces the release of IL-8 from human monocytes and enhances the CSE-induced IL-8 release.

CONCLUSIONS

Humic acid deposition in the lungs potentiates the development of cigarette smoke-induced interstitial inflammation and lung emphysema. Moreover, humic acid promotes IL-8 release from human monocytes. Since humic acid accumulates steadily in the lungs of smokers, this may provide an explanation for the natural history on late onset of this disease. The model described here offers a novel way to study emphysema and may direct the search for new therapeutic approaches.

Antioxidant effects of Panax ginseng C.A. Meyer in healthy subjects: a randomized, placebo-controlled clinical trial

We investigated the antioxidant effects of Panax ginseng C.A. Meyer on healthy volunteers. In a double-blind randomized controlled design, 82 participants (21 men and 61 women) who were considered healthy by both objective and subjective health standard were divided into three groups, the control group and the groups received P. ginseng extract (1 or 2g/day) for 4 weeks. Serum level of reactive oxygen species (ROS), malondialdehyde (MDA), total antioxidant capacity (TAC), the activities of catalase, superoxide dismutase (SOD), glutathione reductase (GSH-Rd), and peroxidase (GSH-Px), and total glutathione content were determined before and after the trial. Administration of P. ginseng led to significant decreases in the levels of serum ROS and MDA. Notably, the total glutathione content and GSH-Rd activity considerably improved in the groups that received 2g of P. ginseng. No significant alterations were observed in TAC, catalase, SOD, and GSH-Px activities. In conclusion, our findings indicate that P. ginseng was shown to have antioxidant property. It enhanced the antioxidant defense mechanism in healthy populations and the results may reinforce the use of P. ginseng as a potential antioxidant supplement.

The emerging role of iron dyshomeostasis in the mitochondrial decay of aging

Recent studies show that cellular and mitochondrial iron increases with age. Iron overload, especially in mitochondria, increases the availability of redox-active iron, which may be a causal factor in the extensive age-related biomolecular oxidative damage observed in aged organisms. Such damage is thought to play a major role in the pathogenesis of iron overload diseases and age-related pathologies. Indeed, recent findings of the beneficial effects of iron manipulation in life extension in Caenorhabditis elegans, Drosophila and transgenic mice have sparked a renewed interest in the potential role of iron in longevity. A substantial research effort now focuses on developing and testing safe pharmacologic interventions to combat iron dyshomeostasis in aging, acute injuries and in iron overload disorders.

Oxidatively damaged DNA induced by humic acid and arsenic in maternal and neonatal mice

We measured the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a useful biomarker of oxidative injury, in liver (or urine) of maternal mice and their offspring, that were treated with humic acid (HA) and arsenic (As) alone, or their combination during pregnancy. A highly sensitive and specific isotope-dilution LC-MS/MS method was used for 8-oxodGuo quantification. Total arsenic accumulated in the offspring was also measured using ICP-MS. This study demonstrated, for the first time in an animal model, that HA alone treatment led to a significant increase of 8-oxodGuo levels both in liver and urine of maternal mice. No enhanced effect was observed when HA was combined with As, compared with the As alone treatment. With regard to the associated offspring, elevated levels of 8-oxodGuo and total arsenic were observed in offspring only when mother mice were treated with As and its combination with HA, but not for the HA-treated alone. It was worthy to note that the offspring from maternal combined treatment with HA and As had a significantly lower 8-oxodGuo than those of maternal treatment with As alone. This could be explained by that part of As formed complexes with HA and these macromolecules of HA-As complexes may not readily cross the placenta to the fetus, as evidenced by the lower accumulated total As observed in the offspring livers. Overall, it seems that HA may be detrimental to the maternal mice, but in the meantime it can be beneficial to the offspring by reducing free As.

Damage to lung epithelial cells and lining fluid antioxidant defense by humic acid

Humic acid causes diseases including lung emphysema and fibrosis. Emerging evidence indicates that oxidative stress is involved in humic acid-induced effects. In the present study, we investigated generation of hydroxyl radicals from humic acid, as well as the effects of humic acid to lung epithelial cells and artificial alveolar lining fluid antioxidant mixture. The involvement of iron in humic acid-induced effects was also determined. We found that humic acid (concentration and time dependently) reduced the cell survival, increased caspase-3 activity, depleted GSH and raised lipid peroxidation in epithelial cells. Humic acid reduced antioxidant levels in the lining fluid antioxidant mix, which could be prevented by adding metal ion chelators. These findings suggest that humic acid causes oxidative stress in lung cells and alveolar lining fluid, which is most likely triggered by hydroxyl radicals produced directly from humic acid. Iron is probably involved in humic acid toxicity.

Humic substances. Part 2: Interactions with organisms

GOAL, SCOPE AND BACKGROUND

Freshwater bodies which chemistry is dominated by dissolved humic substances (HS) seem to be the major type on Earth, due to huge non-calcareous geological formations in the Northern Hemisphere and in the tropics. Based on the paradigm of the inertness of being organic, direct interactions of dissolved HS with freshwater organisms are mostly neglected. However, dissolved organic carbon, the majority of which being HS, are natural environmental chemicals and should therefore directly interact with organisms. Major results that widened our perspective on humic substance ecology come from experiments with the compost nematode, Caenorhabditis elegans, which behaved contradictorily to textbook knowledge and provoked an in-depth re-consideration of some paradigms.

APPROACH

To overcome old paradigms on HS and their potential interactions with organisms, we reviewed recent international literature, as well as 'grey' literature. We also include results from own ongoing studies.

RESULTS

This review focuses on direct interactions of dissolved HS with freshwater organisms and disregards indirect effects, such as under-water light quenching. Instead we show with some macrophyte and algal species that HS adversely interfere with photosynthesis and growth, whereby closely related algal species show different response patterns. In addition to this, HS suppress cyanobacteria more than eukaryotic algae. Quinones in the HS appear to be the effective structure. Furthermore, HS can modulate the offspring numbers in the nematode C. elegans and cause feminization of fish and amphibians--they possess hormone-like properties. The ecological consequences of this potential remain obscure at present. HS also have the potential to act as chemical attractants as shown with C. elegans and exert a mild chemical stress upon aquatic organisms in many ways: induction of molecular chaperons (stress proteins), induction and modulation of biotransformation and anti-oxidant enzymes. Furthermore, they produce an oxidative stress with lipidperoxidation as one clear symptom or even stress defense strategy. Stronger chemical stresses by HS may even lead to teratogenic effects as shown with fish embryos; all physiological responses to HS-mediated stress require energy, which were compensated on the expense of yolk as shown with zebra fish embryos. One Finnish field survey supports the view of a strong chemical stress, as the weight yield in fish species decreases with increasing HS content in the lakes.

DISCUSSION

HS exert a variety of stress symptoms in aquatic and compost organisms. According to current paradigms of ecotoxicology, these symptoms have to be considered adverse, because their compensation consumes energy which is deducted from the main metabolism. However, the nematode C. elegans looks actively for such stressful environments, and this behavior is only understandable in the light of new paradigms of aging mechanisms, particularly the Green Theory of Aging. In this respect, we discuss the mild HS-mediated stress to aquatic and compost organisms. New empirical findings with HS themselves and HS building blocks appear to be consistent with this emerging paradigm and show that the individual lifespan may be expanded. At present the ecological consequences of these findings remain obscure. However, a multiple-stress resistance may be acquired which improves the individual fitness in a fluctuating environment.

CONCLUSIONS

It appears that dissolved HS have to be considered abiotic ecological driving forces, somewhat less obvious than temperature, nutrients, or light.

PERSPECTIVES

The understanding of the ecological control by dissolved humic substances is still fragmentary and needs to be studied in more details.

UV-irradiation induces oxidative damage to mitochondrial DNA primarily through hydrogen peroxide: analysis of 8-oxodGuo by HPLC

Roles of reactive oxygen species (ROS) in damage to mitochondrial DNA (mtDNA) following ultraviolet (UV)-irradiation were investigated in the human hepatoma cell line SK-HEP-1. We altered the intracellular status of ROS by the overexpression of manganese superoxide dismutase (MnSOD) and/or catalase. Using HPLC, we analyzed 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), known as a marker of damage to DNA molecules. UV-irradiation resulted in the accumulation of 8-oxodGuo in these cells. The overexpression of MnSOD enhanced the accumulation of 8-oxodGuo by UV. The co-overexpression of catalase inhibited the accumulation of 8-oxodGuo by UV in MnSOD-transfectants. The overexpression of MnSOD reduced the colony forming capacity in SK-HEP-1 cells and the co-overexpression of catalase with MnSOD stimulated the capacity compared to control. UV-irradiation inhibited the colony forming capacity in these cells; no difference was observed among the capacities of control, MnSOD- and catalase-transfectants. However, the overexpression of MnSOD/catalase significantly rescued the reduction of colony forming capacity by UV-irradiation. Our results suggest that the accumulation of hydrogen peroxide plays a key role in the oxidative damage to mtDNA of UV-irradiated cells, and also that the overexpression of both MnSOD and catalase reduces the mtDNA damage and blocks the growth inhibition by UV. Our results also indicate that the increased activity of MnSOD may lead to a toxic effect on mtDNA by UV-irradiation.

Promoting neoplastic transformation of humic acid in mouse epidermal JB6 Cl41 cells

Humic acid (HA), a group of high-molecular weight polymer, resulting from the decomposition of organic matter has been implicated as a possible etiological factor for Blackfoot disease and cancer. In this study, we evaluate the promotion effect of HA on the transformation in mouse epidermal JB6 clone 41 (JB6 Cl41) cells that have been used to identify the tumor promoting activity of various compounds. Our preliminary assay demonstrated that JB6 Cl41 cells with the treatment of HA at the concentration of 100 microg/ml for 72 and 96 h significantly increased reactive oxygen species (ROS) as compared to the untreated control. In addition, the 48 h cultured cells with HA pretreatment for 48 h also increased ROS as compared to the untreated control. HA-pretreated cells develop highly scattered and spindle-shaped cells with few observable cell-cell contacts, and contain more filopodia. In vitro wound-healing assay showed that JB6 Cl41 cells with HA pretreatment increased the migrating growth. Furthermore, transformed foci of JB6 Cl41 cells following the HA pretreatment were observed after 6 weeks culture. In anchorage-independent growth assay, we found that HA promoted the colony formation and that colonies were inhibited by antioxidant N-acetyl cysteine (NAC). Our results suggest that HA may promote the transformation of epidermal cells and that this process is mediated by the generation of ROS.

Activation of Ah receptor by pure humic acids

Humic substances (HS) are ubiquitous in the environment. However, some studies indicate that HS could induce direct adverse effects on human health and hormone-like effects in fish, amphibians, and invertebrates. In this study we investigated a possible biochemical mechanism of HS toxicity via activation of the aryl hydrocarbon receptor (AhR). AhR mediates the toxic and biological effects of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but a number of structurally diverse compounds has also been found to activate AhR. Alkali solutions of humic acids (HA) were prepared, and subsequently, lipophilic compounds (including parts of HA) were extracted by liquid-liquid extraction with hexane/dichloromethane. Organic extract of HA was further treated with sulfuric acid to study the role of possible trace persistent contaminants. In vitro dioxin-like activities of obtained extract and HA solutions have been evaluated using H4IIE.luc cells by determining the ethoxyresorufin-O-deethylase (EROD) activity and induction of AhR-dependent reporter luciferase. Traces of nonpersistent residues in HA with known AhR activity were identified and quantified by GC-MS. Our results show that an alkali solution as well as organic extract of HA were active in both EROD and luciferase assays, while H2SO4-treated extract activity was negligible. Only nonsignificant levels of AhR-inducing contaminants (PAHs and PCBs) were found in the HA samples. Our results indicate that HA or their fragments can elicit significant inductions of AhR-mediated effects in vitro. To our best knowledge, this study is the first in providing direct evidence of dioxin-like effects of HA. Further efforts should focus on detailed characterization of potential toxic effects of various HSs.

Reactive oxygen species scavenging ability of a new compound derived from weathered coal

The scavenging activity of three fulvic acids (named XWCS-1, XWCS-4, and XWCS-8 according to time taken for ozonolysis) obtained by ozonolysis of humic acid extracted from Xinjiang (China) weathered coal and a fulvic acid (named XWCFA) extracted from the same coal towards reactive oxygen species such as superoxide radical (O(2)(.)(-)) and hydroxyl radical ((.)OH) was investigated with an electron spin resonance (ESR)-spin trapping method using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. O(2)(.)(-) was generated with a hypoxanthine-xanthine oxidase system. (.)OH was generated by three different methods; (i) FeSO(4)-hydrogen peroxide (H(2)O(2)) system, (ii) Cu(en)(2)-H(2)O(2) system, and (iii) UVB photolysis of H(2)O(2). At physiological pH, XWCS-1 had the greatest O(2)(.)(-) scavenging activity, followed by XWCS-4, XWCS-8 and XWCFA. XWCFA had the greatest ?OH scavenging activity among the four fulvic acids, whereas XWCS-1 and XWCS-4 enhanced the production of (.)OH from a metal-catalyzed hydroxyl radical generating system, suggesting that these molecules act as prooxidants in the presence of metal ion.

Humic acid induces oxidative DNA damage, growth retardation, and apoptosis in human primary fibroblasts

Humic acid (HA) has been implicated as an etiological factor of Blackfoot disease endemic in the southwest coast of Taiwan. Dysfunction of endothelial cells and vasculopathy have been proposed to explain the onset of ulcerous changes at extremities. However, little is known about the effect of HA on activities of cells in these nonhealing wounds. In the present study, we demonstrate that HA adversely affects the growth properties of fibroblasts, one of the key players in wound repair. HA treatment caused growth arrest and apoptosis in human foreskin fibroblasts (HFF). This was accompanied by a significant increase in the level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in cellular DNA. The increased fluorescence in dichlorofluorescin (H2DCF)-stained and HA-treated cells suggests the involvement of reactive oxygen species (ROS) in HA-induced biological effects. Conversely, vitamin E pretreatment, which significantly reduced the 8-OHdG formation in HA-treated cells, alleviated the growth-inhibitory and apoptosis-inducing effects of HA. These results indicate that HA initiates oxidative damages to fibroblasts, and leads to their dwindling growth potential and survival. The present study suggests that HA-induced growth retardation and apoptosis of fibroblasts may play a role in the pathogenesis of Blackfoot disease.

A review of fluorescence methods for assessing labile iron in cells and biological fluids

A variety of biochemical, pharmacological, and toxicological properties have been attributed to labile forms of iron that are associated with cells or with biological fluids. Unlike the major fraction of bioiron which is protein bound, the labile bioiron is chelatable and therefore amenable for detection by metal-sensing devices that are coupled to chelation moieties. The present review deals with the detection of various labile forms of iron present in living cells and in fluids of biological interest, in health and disease. The main focus of the review is on the design and application of fluorescent probes as analytical tools for assessing labile iron and iron transport mechanisms and the efficiency of iron chelators in solution and in cellular systems.