Humic acid induces the generation of nitric oxide in human umbilical vein endothelial cells: stimulation of nitric oxide synthase during cell injury.

Humic acid (HA) has been implicated as an etiological factor in the peripheral vasculopathy of blackfoot disease (BFD). In this study, we examined the effects of HA upon the generation of nitric oxide (NO) during the process of lethal cell injury in cultured human umbilical vein endothelial cells (HUVECs). NO production was measured by the formation of nitrite (NO(2)(-)), the stable end-metabolite of NO. Cell death was assessed by measuring the release of intracellular lactate dehydrogenase (LDH). Treatment HUVECs with HA at a concentration of 50, 100, and 200 microg/ml concentration-dependently increased nitrite levels, reaching a peak at 12 h subsequent to HA treatment, with a maximal response of approximately 400 pmole nitrite (from 1 x 10(4) cells). HA-induced nitrite formation was blocked completely by N(G)-nitro-L-arginine methyl ester (L-NAME) and also by N(G)-methyl-L-arginine (L-NMA), both being specific inhibitors of NO synthase. The LDH released from endothelial cells was evoked at from 24 h after the addition of HA (50, 100, 200 microg/ml) in a concentration- and time-dependent manner. The HA-induced LDH release was also reduced by the presence of both L-NAME and L-NMA. The addition of Ca(2+) chelator (BAPTA) inhibited both nitrite formation and LDH release by HA. Moreover, the antioxidants (superoxide dismutase, vitamin C, vitamin E) and protein kinase inhibitor (H7) effectively suppressed HA-induced nitrite formation. These results suggest that HA treatment of endothelial cells stimulates NO production, which can elicit cell injury via the stimulation of Ca(2+)-dependent NO synthase activity by increasing cytosolic Ca(2+) levels. Because the destruction of endothelial cells has been implicated in triggering the onset of BFD, the induction of excessive levels of NO and consequent endothelial-cell injury may be important to the etiology of HA-induced vascular disorders associated with BFD for humans.

Humic acid induces expression of tissue factor by cultured endothelial cells: regulation by cytosolic calcium and protein kinase C.

Blackfoot disease is a thrombotic peripheral vascular disease causally related to the fluorescent humic acid (HA) found in the drinking water of wells in endemic areas in Taiwan. In this study we examined the effect of HA on tissue factor (TF) expression by vascular endothelial cells. Incubation of cultured human umbilical vein endothelial cells (HUVEC) with HA isolated from endemic area drinking water or with a synthetic humic acid polymer (SHA), resulted in enhanced cell surface expression of TF activity by HUVEC. The intracellular calcium level ([Ca2+]i) was measured using a calcium-specific fluorescent probe, fura 2. Changes in [Ca2+]i level were followed and quantitatively analyzed by spectrofluorometric microscopy, after incubation of the fura 2-loaded HUVEC with HA or SHA in a medium containing 1.8 mM CaCl2. Both HA and SHA increased [Ca2+]i in the presence of extracellular calcium ions, but not in their absence, indicating that influx of extracellular Ca2+ occurred during incubation of HUVEC with HA or SHA. Verapamil, a potent calcium channel blocker, did not abolish the enhancement of [Ca2+]i induced by HA or SHA, indicating that specific calcium channels may not be involved in the HA/SHA-induced elevation of [Ca2+]i. The elevated [Ca2+]i level induced by HA or SHA returned to basal level following removal of HA or SHA and incubation of the washed cells in medium containing 1.8 mM CaCl2. All these changes occurred in the absence of significant cytotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutagenic by-products from chlorination of humic acid.

Chlorination of humic and fulvic acid results in the formation of direct-acting mutagenicity, detectable in the Salmonella/microsome assay (Ames test). This mutagenicity is being characterized as part of an overall effort aimed at evaluating potential health risks associated with the presence of mutagenic chemicals in drinking water. A number of chlorinated organic compounds, including several known mutagens, have been identified and quantified in diethyl ether extracts of chlorinated humic acid solutions. However, the total mutagenicity of these compounds accounts for only about 7% of the original mutagenicity. Synergistic or antagonistic interactions among the identified components have been ruled out as possible explanations for the failure to account for a higher percentage of the activity. Recent progress has been made to separate the activity into neutral and strong acid fractions. Further isolation of the strong acids by high-pressure liquid chromatography (HPLC) has resulted in the purification of the mutagenicity into a major peak of activity with a specific mutagenicity of about 20,000 TA100 revertants per milligram. Several trichlorohydroxyfuranone isomers have been tentatively identified in this fraction. The contribution of these types of compounds to the mutagenicity of chlorinated humic acid is under investigation.

A method to remove environmental inhibitors prior to the detection of waterborne enteric viruses by reverse transcription-polymerase chain reaction.

A method was developed to remove environmental inhibitors from sample concentrates prior to detection of human enteric viruses using the reverse transcription-polymerase chain reaction (RT-PCR). Environmental inhibitors, concentrated along with viruses during water sample processing, are removed by the method through a series of steps that includes dialysis, solvent extraction, ultrafiltration and glass purification. The method was tested by spiking sodium phosphate with poliovirus type 1 with or without humic or fulvic acids and then measuring virus recovery by plaque assay and RT-PCR. Results of the study indicated that (i) 90% of the spiked virus could be recovered from samples at the end of the ultrafiltration step, (ii) virus was detected in the final eluate of samples containing as much as 0.5 mg of humic acid or 5.0 mg of fulvic acid, and (iii) as little as 0.06 plaque forming units (PFU) was detectable per RT-PCR reaction. These results indicate that the described purification method along with RT-PCR is a feasible approach for detecting waterborne human enteric viruses in the presence of interfering substances.

Arsenic as a promoter in the effect of humic substances on plasma prothrombin time in vitro.

Protocatechuic acid can be oxidized and polymerized to from humic substances (humic acid and fulvic acid). Should AS2O3 occur in the process of oxidative polymerization, humic acid output can increase by 1.5 - 2.3 times and, in the case of fulvic acid, at least 10 times. After protocatechuic acid is oxidized and polymerized, the resultant humic and fulvic acids both exhibit the ability to shorten the prothrombin time of human pool plasma in vitro. This ability becomes more apparent when AS2O3 serves as a promoter in the course of oxidative polymerization as described above. However, AS2O3 or protocatechuic acid alone is unable to shorten the prothrombin time of human pool plasma.

The effect of fluorescent humic substances existing in the well water of Blackfoot disease endemic areas in Taiwan on prothrombin time and activated partial thromboplastin time in vitro.

Fluorescent humic substances (FHS) in well water of Blackfoot disease endemic areas were purified and fractionated by Sephadex G-25 column chromatography. Four fractions of the purified FHS were isolated. The purified FHS and their fractions were then added to normal human pool plasma in vitro separately to detect the abilities of the effects on prothrombin time (PT) and activated thromboplastin time (APTT). Results showed that all of the four fractions of the purified FHS prolonged both PT and APTT in the higher concentration ranges (10 mg/ml - 20 mg/ml), but shortened both PT and APTT in the lower concentration ranges (0.5 mg/ml - 5 mg/ml). Among the four fractions of the FHS, the fraction 1, the humic substance with the highest molecular weight among all the four FHS, showed the most obvious effects. Owing to the effects of the FHS on PT and APTT values, we supposed that there is a close relationship between the FHS and the cause of Blackfoot disease.

Anti-HSV-1 activity of synthetic humic acid-like polymers derived from p-diphenolic starting compounds.

A panel of ten humic-acid-like polymers was synthesized by oxidation of p-diphenolic compounds and characterized by relative molecular weights, FT-IR spectra and functional group analysis. Using the XTT-based tetrazolium reduction assay EZ4U, both the low-molecular starting compounds and the synthesized polymers were examined for antiviral and cytotoxic activities in HSV-1-infected Vero cells. With the exception of hydroquinone, 2,5-dihydroxytoluene and 2,5-dihydroxybenzoquinone, the starting compounds failed to inhibit herpesvirus replication. The polymeric oxidation products, however, developed anti-HSV-1 activity with EC50 values in the range of 0.65 (2,5-DHPOP) and 322 microg/ml (2,5-DHBQOP). The CC50 values of the polymers varied among 32.0 (TMHYDROP) and >512 microg/ml (2,5-DHBQOP, HYDSULFOP). The most effective polymers were found to be 2,5-DHPOP 2,5-DHTOP and GENOP (EC50: 0.65, 1.6 and 2.2 microg/ml, respectively, and SI: > or = 400, > or = 80 and > or = 58, respectively). Functional group analysis revealed that increasing numbers of carboxyl groups together with a high content of hydroxyl groups tend to enhance the antiviral activity of polymers derived from p-diphenolic compounds.

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.

Inhibition of endogenous thyroid hormone receptor-beta and peroxisome proliferator-activated receptor-alpha activities by humic acid in a human-derived liver cell line.

Humic acid (HA), know to be ubiquitous in the natural environment, is present in almost all soil, surface water, and plants. Earlier studies indicate that HA can affect thyroid economy via binding with iodide, inhibiting both thyroid peroxidase and hepatic 5'-deiodinase in rodents. However, the effect of HA, a peroxisome proliferator in rodents, on thyroid hormone receptor (TR) and peroxisome proliferator-activated receptor (PPAR) in human cells has not yet been examined. In this study, we demonstrate that the malic enzyme activity and the transcriptional activities of endogenous TR and PPAR were inhibited after treatment with HA in human hepatocyte Chang liver cell line. Although the protein expression levels of TR-beta, PPAR-alpha and retinoid X receptor-alpha (RXRalpha) were not changed significantly by HA treatment, both the binding abilities of endogenous TR-beta on thyroid hormone response element (TRE) and PPAR-alpha on the PPAR response element (PPRE) were inhibited by HA treatment. The study of the subcellular distribution of HA, relying on the inherent HA fluorescence, showed that HA distributed in the intracellular compartments including cytoplasm and nucleus. The 50% binding inhibition values (CI(50)) of HA on ME-TRE (malic enzyme gene-TRE) and ACOX-PPRE (acylCoA oxidase gene-PPRE) were 19.31 and 19.94 microg/mL, respectively. These results suggest that HA-induced endemic goiter may link in part to the disruption of TRbeta and PPARalpha function in human Chang liver cells. This model may be useful in the investigation of environmental goitrogens.

Effects of humic substances on fluorometric DNA quantification and DNA hybridization.

DNA extracts from sediment and water samples are often contaminated with coextracted humic-like impurities. Estuarine humic substances and vascular plant extract were used to evaluate the effect of the presence of such impurities on DNA hybridization and quantification. The presence of humic substances and vascular plant extract interfered with the fluorometric measurement of DNA concentration using Hoechst dye H33258 and PicoGreen reagent. Quantification of DNA amended with humic substances (20-80 ng/microl) using the Hoechst dye assay was more reliable than with PicoGreen reagent. A simple procedure was developed to improve the accuracy for determining the DNA concentration in the presence of humic substances. In samples containing up to 80 ng/microl of humic acids, the fluorescence of the samples were measured twice: first without Hoechst dye to ascertain any fluorescence from impurities in the DNA sample, followed with Hoechst dye addition to obtain the total sample fluorescence. The fluorescence of the Hoechst dye-DNA complex was calculated by subtracting the fluorescence of the impurities from the fluorescence of the sample. Vascular plant extract and humic substances reduced the binding of DNA onto the nylon membrane. Low amounts (<2.0 microg) of humic substances derived from estuarine waters did not affect the binding of 100 ng of target DNA to nylon membranes. DNA samples containing 1.0 microg of humic substances performed well in DNA hybridizations with DIG-labeled oliogonucleotide and chromosomal probes. Therefore, we suggest that DNA samples containing low concentrations of humic substances (<20 ng/microl) could be used in quantitative membrane hybridization without further purification.

Tolpa Torf Preparation (TTP) induces interferon and tumor necrosis factor production in human peripheral blood leukocytes.

Tolpa Torf Preparation (TTP) is a natural immunomodulating drug registered in Poland for use in humans. TTP is a biologically active low molecular weight fraction of an extract from peat containing organic substances, primary bound sugars, amino-acids, uronic and huminic acids and mineral salts. The toxicity of TTP is remarkably low, eg. cytotoxicity (CD50) for human peripheral blood leukocytes (PBL) is 1-9 mg/ml. We have discovered that TTP is an interferon (IFN) and tumor necrosis factor (TNF) inducer in human PBL. The IFN and TNF response of the PBL cultures was dose dependent. The optimal concentration of TTP for IFN or TNF response was 10-100 micrograms/ml. The cytokines stimulated by TTP were IFN-gamma, IFN-alpha and TNF-alpha. Ten commercial batches of TTP have been found to be active as cytokines inducers although variations in their activities were observed. On the other hand, 8 batches of TTP rejected by the producer because of the inadequate immunostimulating activity determined in mice, were found to be significantly less active than the commercial preparations. Over 115 buffy coats from the individual blood donors were used to prepare PBL cultures for this study. Approximately 20% of the PBL cultures were unresponsive to TTP. The IFN and TNF response of PBL to other inducers: phytohemagglutinin (PHA) or lipopolysaccharides (LPS) also varied. Whereas only 7% of PBL could not be stimulated by PHA, as much as 20-50% of PBL failed to produce IFN or TNF when treated with LPS. We suggest that TTP may have clinically useful activities connected with the capacity of stimulation of IFNs and TNF production.

A method to assess the immunomodulating effects of the Tolpa Torf Preparation (TTP) by measuring the hyporeactivity to interferon induction and tumor necrosis factor response.

Tolpa Torf Preparation (TTP) is an immunomodulator which was found to be interferon (IFN) and tumor necrosis factor (TNF) inducer in human peripheral blood leukocytes (PBL). PBL cultures prepared from the blood of healthy volunteers taking 5 mg TTP tablet daily loose ability to respond to IFN induction by TTP, phytohemagglutinin (PHA) or lipopolysaccharide (LPS). The phenomenon of hyporeactivity or tolerance is characteristic of every IFN inducer described so far. In the TTP treated volunteers the tolerance developed during three weeks and it lasted one to two weeks. In comparison with the tolerance to the IFN induction the hyporeactivity to TNF induction developed slowly and it was only partial. Because the detection of the tolerance to IFN induction is a very sensitive indicator of TTP activity in vivo in patients taking the drug orally, we suggest that it may be applied to assess the mode of action, dosage and schedule of administration of the IFN-inducing immunomodulator.

Production of cytokines by mouse peritoneal cells treated with Tolpa Torf Preparation (TTP): dependence on age and strain of mice.

Production of two cytokines: Interferon beta (IFN-beta) and tumor necrosis factor alpha (TNF-alpha) by freshly isolated resident mouse peritoneal cells (RPC) treated with immunostimulating drug Tolpa* Torf Preparation (TTP) was investigated. Nontoxic concentrations of TTP (10 and 100 micrograms/ml) potentiated the cytokine production by RPC of BALB/c mice. The observed effects were dose-dependent. The optimal cytokine-inducing concentration of TTP was 100 micrograms/ml. The effect of TTP depended on the age of mice. The high potentiation (16-fold) of IFN-beta and TNF-alpha production by TTP was observed when 5 and 8 week-old mice were used. However, in RPC isolated from one year old mice, only two (fold) potentiation of IFN and TNF was observed. The activities of the same commercial preparations of TTP were compared in the RPC cultures isolated from mice of the three different strains: BALB/c, C3H/HeJ and NZB. The significant stimulation (16-32-fold) of TNF and IFN was observed in the cells isolated from BALB/c mice. In contrast, only slight stimulation of IFN and TNF (1-3-fold) was observed in cells of NZB mice. Peritoneal cells of C3H mice did not respond to stimulation with TTP.

Development and disappearance of tolerance to induction of interferon and tumor necrosis factor response in athletes treated with natural immunostimulant.

The effect of nonspecific immunostimulation was examined in 15 basketball players subjected to extensive physical effort. The Tolpa* Torf Preparation (TTP*), a natural immunostimulating drug, was applied orally, one 5 mg tablet daily, in two 21-day cycles, separated by 2-week hiatus. Blood samples were collected 4 times, after each of two TTP* cycles and after the first and second hiatus. Whole blood assay was used to determine the spontaneous and induced production of interferon (IFN) and tumor necrosis factor (TNF). The levels of the cytokines were measured by microbioassays. TTP* stimulated synthesis of IFN and TNF in the whole blood cultures. However, after the oral administraton of TTP* for 3 weeks the leukocytes of the athletes developed hyporeactivity to IFN induction by TTP* and to a lesser extent to another "superinducer"--a mixture of phytohemagglutinin and bacterial lipopolysaccharide. The hyporeactivity state disappeared spontaneously within 2 weeks. In contrast, the tolerance to TNF induction did not develop during the TTP* administration. The increase of immunoglobulins, mainly of IgM and IgG classes and an acute phase protein--alpha1-antitrypsin, was observed at the late phase of the treatment. We suggest that the cytokine levels may be early markers for immunoprophylaxis. Furthermore, high production of IFN and TNF may be associated with extensive physical effort.

Desmutagenic effect of humic acid.

In the present study, humic acid was not found to be mutagenic and did not inhibit spontaneous mutation. It did, however, inhibit the mutagenicities of benzo[a]pyrene and 3-aminoanthracene (+S9 mix), but not the mutagenicities of 4NQO, AF-2 and MNNG (-S9 mix). 2-Nitrofluorene and 1-nitropyrene do not need S9 mix for activation of their mutagenicities, but an inhibitory effect was observed. Humic acid exerts a desmutagenic effect on mutagens directly before they act on cells. It does not act as an antimutagen which blocks the processes changing normal cells to mutants. The desmutagenic effect was not decreased by heat treatment (120 degrees C, 15 min). Humic acid was fractionated according to molecular weight and the desmutagenic effect increased with an increase in molecular weight. This effect in the fraction with molecular weight exceeding 300 000 was decreased by centrifugation. The desmutagenic ability of humic acid may result from soluble components and adsorption to small particles.

Mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solutions.

The mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solution was assayed with Salmonella typhimurium strains TA97, TA98, TA100, TA102 and TA104 in the presence and absence of S9 mix from phenobarbital- and 5,6-benzoflavone-induced rat liver. Ozonated naphthoresorcinol was mutagenic in TA97, TA98, TA100 and TA104 without S9 mix. By the addition of S9 mix, the mutagenic activity of ozonated naphthoresorcinol was markedly suppressed in TA98 and TA100, but became positive in TA102. High-performance liquid chromatography (HPLC) after derivatization to 2,4-dinitrophenylhydrazones demonstrated the formation of glyoxal as an ozonation product of naphthoresorcinol. Ion chromatographic technique also demonstrated the formation of o-phthalic acid, muconic acid, maleic acid, mesoxalic acid, glyoxylic acid and oxalic acid as ozonation products. The mutagenicity assays of these identified products with five Salmonella showed that glyoxal and glyoxylic acid were directly mutagenic; the former in TA100, TA102 and TA104, the latter in TA97, TA100 and TA104. In the presence of S9 mix, glyoxylic acid gave a positive response of mutagenicity for TA102. The experimental evidence supported that glyoxal and glyoxylic acid may contribute to the mutagenicity of ozonated naphthoresorcinol.

Buthionine sulfoximine prevents the reduction of the genotoxic activity of maleic hydrazide by soil humic substances in Vicia faba seedlings.

A significant reduction of the genotoxic effects caused by herbicide maleic hydrazide (MH) in Vicia faba seedlings was observed to be induced by a growth step in an organic soil as well as by a pretreatment with highly purified humic substances. In addition, such protective activity was resulted quite similar to that observed when the conditioning pretreatment was carried out with metal salts, so suggesting the involvement of the GSH biosynthesis in determining the protective activity observed. In agreement with this hypothesis, a previous exposure to buthionine sulfoximine (BSO), an inhibitor of the phytochelatins production, through the inhibition of GSH synthesis, prevented the reduction of the genotoxic activity of MH. The findings provide evidence for the involvement of the GSH biosynthesis pathway in determining the antigenotoxic activity revealed and suggest a possible involvement of the phytochelatins in this process. However, yet to be clarified is whether the stimulation of GSH production results as a consequence of a nonspecific influence on the protein synthesis by humic substances or of its direct activation due to the presence, as contaminants, of some heavy metals in both organic soil and humic acids extracts.

Effects of humic acids, para-aminobenzoic acid and ascorbic acid on the N-nitrosation of the carbamate insecticide propoxur and on the mutagenicity of nitrosopropoxur.

Nitrosation of the carbamate insecticide propoxur at pH 3 and 37 degrees C was determined colorimetrically and found to be time- and sodium nitrite concentration-dependent. Nitrosated propoxur was mutagenic when exposed to the seeds of the higher plant Arabidopsis thaliana but the formation of nitrosopropoxur, the presumed mutagen, was inhibited by humic acids, para-aminobenzoic acid and ascorbic acid. These agents also reduced the mutagenicity of preformed nitrosopropoxur.

Mechanism of the desmutagenic effect of humic acid.

The mechanism of an apparent desmutagenic effect of humic acid was investigated. Firstly, components of humic acid (resorcinol, vanillin, vanillic acid, ferulic acid, protochatechuic acid and benzoic acid) were tested and were not found to show a desmutagenic effect. By contrast, lignin did show a desmutagenic effect. The desmutagenic effect of humic acid was decreased by ozone treatment, and the degree of decrease corresponded with a decrease in KMnO4 consumption. Benzo[a]pyrene and humic acid were incubated at 37 degrees C for 1 h and extracted by ethyl acetate and the extract was investigated by gas chromatography (GC). The peak of the decomposition product did not appear, but the amount of benzo[a]pyrene was decreased. This suggests that the desmutagenic effect of humic acid was caused by adsorption of benzo[a]pyrene by humic acid rather than by decomposition of benzo[a]pyrene. Humic acid had the largest adsorption activity at its critical micelle concentration (CMC), while adsorbed benzo[a]pyrene could be released by ultrasonication. Fulvic acid and water-soluble humic substance showed a slight inhibitory effect on the mutagenicity of benzo[a]pyrene.

Desmutagenic activity of natural humic acids: inhibition of mitomycin C and maleic hydrazide mutagenicity.

Humic acids are natural components of organic matter widespread in the environment. In spite of the incomplete knowledge about their composition, increasing interest in humic acid activity is justified by their ubiquity. Four different humic acids have been tested in Chinese hamster ovary cells in vitro, both alone and in combination with two well-known mutagens (mitomycin C and maleic hydrazide). Data about sister-chromatid exchanges, mitotic and proliferation indices were collected. Our results, on the whole, indicate: (i) a slight mutagenicity and toxicity of tested humic acids, probably due to chlorination during sample preparation; (ii) a desmutagenic rather than antimutagenic activity of the tested humic acids.