Quantitative analysis of catechol and 4-methylcatechol in human urine

A critical examination of human data for the biological activity of quercetin and its phase-2 conjugates

This critical review examines evidence for beneficial effects of quercetin phase-2 conjugates from clinical intervention studies, volunteer feeding trials, and in vitro work. Plasma concentrations of quercetin-3-O-glucuronide (Q3G) and 3'-methylquercetin-3-O-glucuronide (3'MQ3G) after supplementation may produce beneficial effects in macrophages and endothelial cells, respectively, especially if endogenous deglucuronidation occurs, and lower blood uric acid concentration via quercetin-3'-O-sulfate (Q3'S). Unsupplemented diets produce much lower concentrations (<50 nmol/l) rarely investigated in vitro. At 10 nmol/l, Q3'S and Q3G stimulate or suppress, respectively, angiogenesis in endothelial cells. Statistically significant effects have been reported at 100 nmol/l in breast cancer cells (Q3G), primary neuron cultures (Q3G), lymphocytes (Q3G and3'MQ3G) and HUVECs (QG/QS mixture), but it is unclear whether these translate to a health benefit in vivo. More sensitive and more precise methods to measure clinically significant endpoints are required before a conclusion can be drawn regarding effects at normal dietary concentrations. Future requirements include better understanding of inter-individual and temporal variation in plasma quercetin phase-2 conjugates, their mechanisms of action including deglucuronidation and desulfation both in vitro and in vivo, tissue accumulation and washout, as well as potential for synergy or antagonism with other quercetin metabolites and metabolites of other dietary phytochemicals.

Identification of Urinary Food Intake Biomarkers for Milk, Cheese, and Soy-Based Drink by Untargeted GC-MS and NMR in Healthy Humans

The measurement of food intake biomarkers (FIBs) in biofluids represents an objective tool for dietary assessment. FIBs of milk and cheese still need more investigation due to the absence of candidate markers. Thus, an acute intervention study has been performed to sensitively and specifically identify candidate FIBs. Eleven healthy male and female volunteers participated in the randomized, controlled crossover study that tested a single intake of milk and cheese as test products, and soy-based drink as a control. Urine samples were collected at baseline and up to 24 h at distinct time intervals (0-1, 1-2, 2-4, 4-6, 6-12, and 12-24 h) and were analyzed using an untargeted multiplatform approach (GC-MS and ¹H NMR). Lactose, galactose, and galactonate were identified exclusively after milk intake while for other metabolites (allantoin, hippurate, galactitol, and galactono-1,5-lactone) a significant increase has been observed. Urinary 3-phenyllactic acid was the only compound specifically reflecting cheese intake although alanine, proline, and pyroglutamic acid were found at significantly higher levels after cheese consumption. In addition, several novel candidate markers for soy drink were identified, such as pinitol and trigonelline. Together, these candidate FIBs of dairy intake could serve as a basis for future validation studies under free-living conditions.

Modulation of urinary siderophores by the diet, gut microbiota and inflammation in mice

Mammalian siderophores are believed to play a critical role in maintaining iron homeostasis. However, the properties and functions of mammalian siderophores have not been fully clarified. In this study, we have employed Chrome Azurol S (CAS) assay which is a well-established method for bacterial siderophores study, to detect and quantify mammalian siderophores in urine samples. Our study demonstrates that siderophores in urine can be altered by diet, gut microbiota and inflammation. C57BL/6 mice, fed on plant-based chow diets which contain numerous phytochemicals, have more siderophores in the urine compared to those fed on purified diets. Urinary siderophores were up-regulated in iron overload conditions, but not altered by other tested nutrients status. Further, germ-free mice displayed 50% reduced urinary siderophores, in comparison to conventional mice, indicating microbiota biotransformation is critical in generating or stimulating host metabolism to create more siderophores. Altered urinary siderophores levels during inflammation suggest that host health conditions influence systemic siderophores level. This is the first report to measure urinary siderophores as a whole, describing how siderophores levels are modulated under different physiological conditions. We believe that our study opens up a new field in mammalian siderophores research and the technique we used in a novel manner has the potential to be applied to clinical purpose.

4: Final Report on the Safety Assessment of Hydroquinone and Pyrocatechol

Hydroquinone and Pyrocatechol, two benzenediol isomers, are used as couplers in oxidative hair dyes at concentrations of less than 1.0%. Both compounds are absorbed from the gastrointestinal tract; Pyrocatechol is also readily absorbed through the skin. Both compounds are excreted in the urine, mainly as the ethereal sulfate. In acute oral studies Hydroquinone is practically nontoxic to moderately toxic; the data from subchronic feeding studies of Hydroquinone indicated that it was not toxic at 1% but was at higher concentrations. Pyrocatechol was moderately toxic in acute studies. Subchronic oral studies of Pyrocatechol at 0.25% produced hepatic cell hyperplasia in rats. Hydroquinone was a weak depigmenter but not an irritant when tested at 1.0%. Theingredient was a sensitizer when injected at 2.0%. The acute dermal LD50 of Pyrocatechol was 0.8 g/kg. Pyrocatechol did not depigment rabbit skin at 1.0% but did at 3.0%; skin irritation was observed at 5.0%. Guinea pigs were sensitized when Pyrocatechol was injected at concentrations above 0.2 μM. Undiluted product formulation containing 2.0% Hydroquinone produced mild conjunctivitis in 3 of 6 animals; undiluted Pyrocatechol is an extreme ocular irritant.

Hydroquinone was not teratogenic in three separate studies. The results of mutagenesis assays of Hydroquinone varies with the assay system used. In four Salmonella typhimurium strains, both with and without activation, the mutagenesis assay was negative. Hydroquinone produced positive results both with and without activation in the HeLa DNA synthesis test but was not considered mutagenic in assays using Chinese hamster cells. Hydroquinone induced SCE and delayed cell-turnover time in human lymphocyte studies. Oral doses of Hydroquinone did not inhibit testicular DNA synthesis in male mice, and was nonmutagenic in the mouse sperm-head abnormality test. In multigeneration studies with rats, topically applied hair dyes containing 0.2% Hydroquinone had no effect on reproduction; the dye was neither embryotoxic or teratogenic. Dermally applied hair dyes containing Hydroquinone were not carcinogenic. Hydroquinone when applied topically was neither a tumor promoter nor a cocarcinogen in mice. The mutagenicity of Pyrocatechol also varies with the test system used. In most studies, Pyrocatechol was nonmutagenic, both with and without metabolic activation, in the Ames' assay. The compound was negative in the Escherichia coli DNA polymerase assay, but was positive in the yeast, Saccharomyces cerevisiae. Pyrocatechol was negative in the HeLa DNA synthesis test and with Chinese Hamster V79 cells. The compound increased the numbers of chromatid breaks and exchanges in Chinese hamster ovary cells and induced SCE and delayed cell turnover time in human lymphocyte cultures. The compound given by intraperitoneal injection to mice was negative in the sperm-head abnormality test but was positive in the bone marrow assay.

In three studies in mice, topically applied Pyrocatechol was not a tumor promotor. However, topically applied Pyrocatechol was a cocarcinogen for mouse skin in two other studies. Positive sensitization reactions to Hydroquinone were reported in 8.9% of 536 dermatologic patients. Two of 38 patients treated with an ointment containing 5.4% Hydroquinone became sensitized. A cosmetic formulation containing 2% Hydroquinone produced one or more mild irritation reactions in 69 of 90 subjects in the induction phase of a sensitization test; 22 of the 69 subjects were mildly sensitized when challenged. The use of ointments containing 2, 3, and 5% Hydroquinone produced at least minimal depigmentation in white but not black subjects. It is concluded that Hydroquinone and Pyrocatechol are safe for cosmetic use at concentrations of ≤ 1.0% in formulations that are designed for discontinuous, brief use followed by rinsing from the skin and hair.

Human Urinary Composition Controls Antibacterial Activity of Siderocalin

During Escherichia coli urinary tract infections, cells in the human urinary tract release the antimicrobial protein siderocalin (SCN; also known as lipocalin 2, neutrophil gelatinase-associated lipocalin/NGAL, or 24p3). SCN can interfere with E. coli iron acquisition by sequestering ferric iron complexes with enterobactin, the conserved E. coli siderophore. Here, we find that human urinary constituents can reverse this relationship, instead making enterobactin critical for overcoming SCN-mediated growth restriction. Urinary control of SCN activity exhibits wide ranging individual differences. We used these differences to identify elevated urinary pH and aryl metabolites as key biochemical host factors controlling urinary SCN activity. These aryl metabolites are well known products of intestinal microbial metabolism. Together, these results identify an innate antibacterial immune interaction that is critically dependent upon individualistic chemical features of human urine.

Purification and Structural Characterization of "Simple Catechol", the NGAL-Siderocalin Siderophore in Human Urine

The identification of ligands that bind the protein Neutrophil Gelatinase-Associated Lipocalin (NGAL, Siderocalin, Lipocalin-2) have helped to elucidate its function. NGAL-Siderocalin binds and sequesters the iron loaded bacterial siderophore enterochelin (Ent), defining the protein as an innate immune effector. Simple metabolic catechols can also form tight complexes with NGAL-Siderocalin and ferric iron, suggesting that the protein may act as an iron scavenger even in the absence of Ent. While different catechols have been detected in human urine, they have not been directly purified from a biofluid and demonstrated to ligate iron with NGAL-Siderocalin. This paper describes a "natural products" approach to identify small molecules that mediate iron binding to NGAL-Siderocalin. A 10K filtrate of human urine was subjected to multiple steps of column chromatography and reverse-phase HPLC, guided by NGAL-Siderocalin-iron binding assays and LC-MS detection. The co-factor forming a ternary structure with iron and NGAL-Siderocalin was identified as authentic simple catechol (dihydroxybenze) by ESI-HR-Mass, UV, and NMR spectrometric analysis. Comparison of the binding strengths of different catechols demonstrated that the vicinal-dihydroxyl groups were the key functional groups and that steric compatibilities of the catechol ring have the strongest effect on binding. Although catechol was a known NGAL-Siderocalin co-factor, our purification directly confirmed its presence in urine as well as its capacity to serve as an iron trap with NGAL-Siderocalin.

Low-dose metabolism of benzene in humans: science and obfuscation

Benzene is a ubiquitous air pollutant that causes human leukemia and hematotoxic effects. Although the mechanism by which benzene causes toxicity is unclear, metabolism is required. A series of articles by Kim et al. used air and biomonitoring data from workers in Tianjin, China, to investigate the dose-specific metabolism (DSM) of benzene over a wide range of air concentrations (0.03-88.9 p.p.m.). Kim et al. concluded that DSM of benzene is greatest at air concentrations <1 p.p.m. This provocative finding motivated the American Petroleum Institute to fund a study by Price et al. to reanalyze the original data. Although their formal 'reanalysis' reproduced Kim's finding of enhanced DSM at sub-p.p.m. benzene concentrations, Price et al. argued that Kim's methods were inappropriate for assigning benzene exposures to low exposed subjects (based on measurements of urinary benzene) and for adjusting background levels of metabolites (based on median values from the 60 lowest exposed subjects). Price et al. then performed uncertainty analyses under alternative approaches, which led them to conclude that '… the Tianjin data appear to be too uncertain to support any conclusions …' regarding the DSM of benzene. They also argued that the apparent low-dose metabolism of benzene could be explained by 'lung clearance.' In addressing these criticisms, we show that the methods and arguments presented by Price et al. are scientifically unsound and that their results are unreliable.

NGAL-Siderocalin in kidney disease

Kidney damage induces the expression of a myriad of proteins in the serum and in the urine. The function of these proteins in the sequence of damage and repair is now being studied in genetic models and by novel imaging techniques. One of the most intensely expressed proteins is lipocalin2, also called NGAL or Siderocalin. While this protein has been best studied by clinical scientists, only a few labs study its underlying metabolism and function in tissue damage. Structure-function studies, imaging studies and clinical studies have revealed that NGAL-Siderocalin is an endogenous antimicrobial with iron scavenging activity. This review discusses the "iron problem" of kidney damage, the tight linkage between kidney damage and NGAL-Siderocalin expression and the potential roles that NGAL-Siderocalin may serve in the defense of the urogenital system. This article is part of a Special Issue entitled: Cell Biology of Metals.

Iron traffics in circulation bound to a siderocalin (Ngal)-catechol complex

The lipocalins are secreted proteins that bind small organic molecules. Scn-Ngal (also known as neutrophil gelatinase associated lipocalin, siderocalin, lipocalin 2) sequesters bacterial iron chelators, called siderophores, and consequently blocks bacterial growth. However, Scn-Ngal is also prominently expressed in aseptic diseases, implying that it binds additional ligands and serves additional functions. Using chemical screens, crystallography and fluorescence methods, we report that Scn-Ngal binds iron together with a small metabolic product called catechol. The formation of the complex blocked the reactivity of iron and permitted its transport once introduced into circulation in vivo. Scn-Ngal then recycled its iron in endosomes by a pH-sensitive mechanism. As catechols derive from bacterial and mammalian metabolism of dietary compounds, the Scn-Ngal-catechol-Fe(III) complex represents an unforeseen microbial-host interaction, which mimics Scn-Ngal-siderophore interactions but instead traffics iron in aseptic tissues. These results identify an endogenous siderophore, which may link the disparate roles of Scn-Ngal in different diseases.

Biomarker Research in Occupational Health

OBJECTIVES

A variety of biomarkers have been used to study worker populations, and these studies have achieved different levels of success in the improvement of occupational health.

METHODS

Successful application of biomarker research is dependent upon several important factors: ability to identify hazardous substances from the exposure to a variety of substances, relevance to the development of disease, and usefulness for health risk assessment.

RESULTS

Besides the traditional biomarkers for exposure, biological effects, and health risk, new biomarkers for susceptibility and genome-wide responses are being used to improve our understanding of occupational health at a higher and, perhaps, more precise level.

CONCLUSIONS

In addition, there is a continued need to develop and apply biomarkers that can be used to provide real-time detection of excessive exposure to hazardous substances in the workplace, especially from unexpected fugitive emissions. These topics are discussed in the review.

ASSESSMENT OF CATECHOL INDUCTION AND GLUCURONIDATION IN RAT LIVER MICROSOMES

Catechols are substances with a 1,2-dihydroxybenzene group from natural or synthetic origin. The aim of this study was to determine whether catechols (4-methylcatechol, 4-nitrocatechol, 2,3-dihydroxynaphthalene) and the antiparkinsonian drugs, entacapone and tolcapone, at doses 150 to 300 mg/kg/day, for 3 days, are able to enhance their own glucuronidation. The induction potency of catechols on rat liver UDP-glucuronosyltransferases (UGTs) was compared with that of a standard polychlorinated biphenyl (PCB) inducer, Aroclor 1254. The glucuronidation rate of these catechols was enhanced up to 15-fold in the liver microsomes of PCB-treated rats, whereas treatment with catechols had little effect. Entacapone, tolcapone, 4-methylcatechol, catechol, 2,3-dihydroxynaphthalene, and 4-nitrocatechol were glucuronidated in control microsomes at rates ranging from 0.12 for entacapone to 22.0 nmol/min/mg for 4-nitrocatechol. Using 1-naphthol, entacapone, and 1-hydroxypyrene as substrates, a 5-, 8-, and 16-fold induction was detected in the PCB rats, respectively, whereas the catechol-induced activities were 1.1- to 1.5-fold only. Entacapone was glucuronidated more efficiently by PCB microsomes than by control microsomes (Vmax/Km, 0.0125 and 0.0016 ml/min/mg protein, respectively). Similar kinetic results were obtained for 1-hydroxypyrene. The Eadie-Hofstee plots suggested the contribution of multiple UGTs for the glucuronidation of 1-hydroxypyrene (Km1, Km2, Km3 = 0.8, 9.7, and 63 microM, and Vmax1, Vmax2, Vmax3 = 11, 24, and 55 nmol/min/mg, respectively), whereas only one UGT could be implicated in the glucuronidation of entacapone (Km = 130 microM, Vmax = 1.6 nmol/min/mg). In conclusion, catechols are poor inducers of their own glucuronidation supported by several UGT isoforms. Their administration is unlikely to affect the glucuronidation of other drugs administered concomitantly.

Rapid determination of six urinary benzene metabolites in occupationally exposed and unexposed subjects

A gas chromatography-mass spectrometry method for measurement of the main urinary metabolites of benzene, namely, phenol, catechol, hydroquinone, 1,2,4-trihydroxybenzene (trihydroxybenzene), t,t-muconic acid (muconic acid), and S-phenylmercapturic acid (phenylmercapturic acid), is reported. The method is considerably simpler than existing assays. It was applied to urine from benzene-exposed subjects and controls from Shanghai, China. When subjects were divided into controls (n = 44), those exposed to </= 31 ppm benzene (n = 21), and those exposed to > 31 ppm benzene (n = 19), Spearman correlations with exposure category were >/= 0.728 (p < 0.0001) for all metabolites except trihydroxybenzene. When exposed subjects were compared on an individual basis, all metabolites, including trihydroxybenzene, were significantly correlated with benzene exposure (Pearson r >/= 0.472, p </= 0.002) and with each other (Pearson r >/= 0.708, p < 0.0001). Ratios of individual metabolite levels to total metabolite levels provided evidence of competitive inhibition of CYP 2E1 enzymes leading to increased production of phenol, catechol, and phenylmercapturic acid at the expense of hydroquinone, trihydroxybenzene, and muconic acid. Since all metabolites were detected in all control subjects, the method can be applied to persons exposed to environmental levels of benzene.

Human urinary carcinogen metabolites: biomarkers for investigating tobacco and cancer

Measurement of human urinary carcinogen metabolites is a practical approach for obtaining important information about tobacco and cancer. This review presents currently available methods and evaluates their utility. Carcinogens and their metabolites and related compounds that have been quantified in the urine of smokers or non-smokers exposed to environmental tobacco smoke (ETS) include trans,trans-muconic acid (tt-MA) and S-phenylmercapturic acid (metabolites of benzene), 1- and 2-naphthol, hydroxyphenanthrenes and phenanthrene dihydrodiols, 1-hydroxypyrene (1-HOP), metabolites of benzo[a]pyrene, aromatic amines and heterocyclic aromatic amines, N-nitrosoproline, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronides (NNAL and NNAL-Gluc), 8-oxodeoxyguanosine, thioethers, mercapturic acids, and alkyladenines. Nitrosamines and their metabolites have also been quantified in the urine of smokeless tobacco users. The utility of these assays to provide information about carcinogen dose, delineation of exposed vs. non-exposed individuals, and carcinogen metabolism in humans is discussed. NNAL and NNAL-Gluc are exceptionally useful biomarkers because they are derived from a carcinogen- 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)- that is specific to tobacco products. The NNAL assay has high sensitivity and specificity, which are particularly important for studies on ETS exposure. Other useful assays that have been widely applied involve quantitation of 1-HOP and tt-MA. Urinary carcinogen metabolite biomarkers will be critical components of future studies on tobacco and human cancer, particularly with respect to new tobacco products and strategies for harm reduction, the role of metabolic polymorphisms in cancer, and further evaluation of human carcinogen exposure from ETS.

Dose-dependent induction of glandular stomach preneoplastic and neoplastic lesions in male F344 rats treated with catechol chronically

The dose-dependence of catechol glandular stomach carcinogenesis was investigated in male F344 rats. Groups of 30 male animals were fed catechol at dietary levels of 0 (control). 0.1, 0.2, 0.4, and 0.8% for up to 104 weeks. Five rats of each group were killed at 34 weeks and the remaining animals were sacrificed at the termination, all undergoing histopathological examination. Moderate retardation of body weight increase was observed in the 0.8% group. but no adverse effects were found in terms of survival. Submucosal hyperplasias and adenomas of the pyloric glands developed in the 0.4 and 0.8% groups, only very minor changes being noted in the 0.1 and 0.2% groups at week 34. Incidences of adenocarcinoma development in the pylorus were 4% and 8% in 0.4% and 0.8% groups, respectively, and 0 in the 0.1% and 0.2% groups, at the termination. Adenomas and submucosal hyperplasias were found in nearly all animals fed 0.2% catechol or more, the incidences of those in 0.1% group being 0% and 56%, respectively. Serum gastrin levels were significantly increased in the 0.2, 0.4, and 0.8% groups at 34 weeks, and in all treated groups at the termination, at extents comparable with the induction of proliferative lesions in the pylorus. The results thus demonstrated that dietary levels of 0.4% and 0.8% catechol long-term induce adenocarcinomas in the pyloric glands, while 0.1 and 0.2% cause benign proliferative lesions, all accompanied by increase in serum gastrin levels. As a no-effect level could not be decided in the present study, further investigation of lower doses is needed to determine whether a threshold exists.

Urinary benzene as a biomarker of exposure among occupationally exposed and unexposed subjects

Urinary benzene (UB) was investigated as a biomarker of exposure among benzene-exposed workers and unexposed subjects in Shanghai, China. Measurements were performed via headspace solid phase microextraction of 0.5 ml of urine specimens followed by gas chromatography-mass spectrometry. This assay is simple and more sensitive than other methods (detection limit 0.016 microg benzene/l urine). The median daily benzene exposure was 31 p.p.m. (range 1.65-329 p.p.m.). When subjects were divided into controls (n = 41), those exposed to < or =31 p.p.m. benzene (n = 22) and >31 p.p.m. benzene (n = 20), the median UB levels were 0.069, 4.95 and 46.1 microg/l, respectively (Spearman r = 0.879, P < 0.0001). A linear relationship was observed between the logarithm of UB and the logarithm of benzene exposure in exposed subjects according to the following equation: ln(UB, microg/l) = 0.196 + 0.709 ln (exposure, p.p.m.) (r = 0.717, P < 0.0001). Considering all subjects, linear relationships were also observed between the logarithm of UB and the corresponding logarithms of four urinary metabolites of benzene, namely t,t-muconic acid (r = 0.938, P < 0.0001), phenol (r = 0.826, P < 0.0001), catechol (r = 0.812, P < 0.0001) and hydroquinone (r = 0.898, P: < 0.0001). Ratios of individual metabolite levels to total metabolites versus UB provide evidence of competitive inhibition of CYP450 enzymes leading to increased production of phenol and catechol at the expense of hydroquinone and muconic acid. Among control subjects UB was readily detected with a mean level of 0.145 microg/l (range 0.027-2.06 microg/l), compared with 5.63 microg/l (range 0.837-26.38 microg/l) in workers exposed to benzene below 10 p.p.m. (P < 0.0001). This suggests that UB is a good biomarker for exposure to low levels of benzene.

Hypothesis: phenol and hydroquinone derived mainly from diet and gastrointestinal flora activity are causal factors in leukemia

High background levels of phenol and hydroquinone are present in the blood and urine of virtually all individuals, but vary widely. Phenol and hydroquinone have been strongly implicated in producing leukemia associated with benzene exposure, because they reproduce the hematotoxicity of benzene, cause DNA and chromosomal damage found in leukemia, inhibit topoisomerase II, and alter hematopoiesis and clonal selection. The widely varying background levels of phenol and hydroquinone in control individuals stem mainly from direct dietary ingestion, catabolism of tyrosine and other substrates by gut bacteria, ingestion of arbutin-containing foods, cigarette smoking, and the use of some over-the-counter medicines. We hypothesize that these background sources of phenol and hydroquinone and associated adducts play a causal role in producing some forms of de novo leukemia in the general population. This hypothesis is consistent with recent epidemiological findings associating leukemia with diets rich in meat and protein, the use of antibiotics (which change gastrointestinal flora make-up), lack of breastfeeding, and low activity of NAD(P)H quinone oxidoreductase which detoxifies quinones derived from phenol and hydroquinone and protects against benzene hematotoxicity. An attractive feature of our hypothesis is that it may explain why many people who have no known occupational exposures or significant smoking history develop leukemia. The hypothesis predicts that susceptibility to the disease would be related to diet, medicinal intake, genetics and gut-flora composition. The latter two of these are largely beyond our control, and thus dietary modification and reduced use of medicines that elevate phenol levels may be the best intervention strategies for lowering leukemia risk.

Sequential morphological and biological changes in the glandular stomach induced by oral administration of catechol to male F344 rats

Histogenesis and mechanisms of catechol-induced rat glandular stomach carcinogenesis were investigated in male F344 rats. Groups of 5 or 6 rats were treated with dietary catechol at doses of 1, 0.5, 0.1, and 0.01% for 12 hr or for 1, 2, 3, or 7 days or at a dose of 0.8% for 1, 2, 4, 12, and 24 wk; rats were then euthanatized. The initial morphological changes were edema of the gastric wall, inflammatory-cell infiltration, erosion in the pyloric region close to the duodenum, and considerable increase in apoptosis at 12 hr; later, changes included augmented DNA synthesis and cell proliferation, as evaluated by bromodeoxyuridine labeling index and thickness of mucosa, respectively, on day 1. Downward hyperplasia due to excess regeneration appeared at edges of ulceration at week 2. This lesion disappeared, and then submucosal hyperplasia appeared in the course of adenoma development. Only slight expression of c-myc or c-fos was apparent after 30-min oral administration or 1-, 3-, and 6-hr oral administration of catechol. No increase in lipid peroxide levels was evident in gastric epithelium fed catechol for 1 wk. The amount of catechol distributed in the glandular stomach and forestomach epithelium, which is not a target for carcinogenesis, did not differ 1, 3, 6, and 24 hr after a single intragastric dose of 75 mg/kg body weight. Amounts of catechol bound to tissue protein were also not specifically high in the glandular stomach. These results indicate that regenerative cell proliferation due to toxicity plays an important role in catechol-induced glandular stomach carcinogenesis. Protein binding and free radicals may not be largely responsible for the toxicity.

Effects of low dose catechol on glandular stomach carcinogenesis in BALB/c mice initiated with N-methyl-N-nitrosourea

The effects of low dose catechol administration in the diet on stomach carcinogenesis in mice after initiation with N-methyl-N-nitrosourea (MNU) in the drinking water were investigated. Male, 6-week-old, BALB/c mice were given MNU in the drinking water intermittently for 1-week periods at 1-week intervals for a total of 3 weeks at a concentration of 120 ppm (groups 1 and 3). Groups 2 and 4 served as non-initiated controls. From week 7, groups 1 and 3 were divided into four subgroups and the mice were fed on a diet containing 4 ppm (groups la and 3a), 20 ppm (groups 1b and 3b), 100 ppm (groups 1c and 3c), 500 ppm (groups 1d and 3d) or 0 ppm (groups 2 and 4) catechol for 44 weeks. At week 50, appreciably enhanced development of pepsinogen 1 altered pyloric glands (PAPG) was noted in groups 1c and 1d. The incidences of adenomatous hyperplasia and carcinomas were not affected in any of the catechol-treated groups as compared with corresponding controls on a basal diet. Thus, the administration of catechol in the diet at low doses enhanced only preneoplastic lesion development and not neoplastic lesion development. From these results, we conclude that the biological significance of the catechol promoting effect at probable human exposure levels on gastric cancer is probably limited, while the PAPG may be a sensitive endpoint lesion for mouse glandular stomach carcinogenesis.

A new assay for albumin and hemoglobin adducts of 1,2- and 1,4-benzoquinones

A new method has been developed to detect mono-S-substituted cysteinyl adducts of 1,2- and 1,4-benzoquinone (BQ) in hemoglobin (Hb) and albumin (Alb). After reacting the protein with trifluoroacetic anhydride and methanesulfonic acid, the resulting isomers of O,O',S-tris-trifluoroacetyl-hydroquinone and -catechol are extracted and detected by gas-chromatography-mass spectrometry in the negative-ion chemical ionization mode. The limit of detection of the assay is about 20 pmol adduct/g protein. This assay was employed to quantitate mono-S-substituted background adducts in human and rat Hb and Alb and benzene-specific adducts in Hb and Alb from F344 rats following a single oral dosage of 50-400 mg [13C6]benzene/kg body wt. In Alb, a dose-related increase in both [13C6]1,2- and [13C6]1,4-BQ adducts was observed with [[13C6]]1,4-BQ-Alb] >> [[13C6]1,2-BQ-Alb]. The formation of [13C6]1,2-BQ-Alb was linear with increasing dosage of benzene with a slope of 2.3 (pmol adduct/g protein)/(mg/kg body wt.) (S.E. = 0.18, R2 = 0.91). However, at dosages above about 100 mg [13C6]benzene/kg body wt., the levels of 1,4-BQ-Alb were greater than proportional to the dosage. Mono-S-substituted adducts of [13C6]1,2-BQ and [13C6]1,4-BQ were not detected in Hb. The background ([12C6]) adducts of 1,2- and 1,4-BQ in 20 F344 rats were estimated (in nmol adduct/g of protein) to be 3.9 (S.E. = 0.23) and 4.9 (S.E. = 0.30) in Hb and 2.7 (S.E. = 0.24) and 11.4 (S.E. = 0.60) in Alb. At the highest dosage of 400 mg [13C6]benzene/kg body wt., background levels of 1,2-BQ-Alb were about 4-fold higher than those of the benzene-specific adducts whereas the benzene-specific levels of 1,4-BQ-Alb were about 7-fold higher than those of the background adducts. Background levels of 1,2- and 1,4-BQ adducts in 10 portions of commercial human proteins were found to be (in nmol adduct/g of protein) 1.6 (S.E. = 0.05) and 0.85 (S.E. = 0.04) in Hb and 1.6 (S.E. = 0.06) and 8.9 (S.E. = 0.36) in Alb.

Effects of catechol, sodium chloride and ethanol either alone or in combination on gastric carcinogenesis in rats pretreated with N-methyl-N'-nitro-N-nitrosoguanidine

Combined effects of catechol, sodium chloride (NaCl) and ethanol on the post-initiation stage of gastric carcinogenesis were examined in rats pretreated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). F344 male rats were given a single intragastric dose of 150 mg/kg b.w. MNNG at 6 weeks of age. Starting 1 week thereafter, groups of 15 rats were administered 0.8% catechol, 5% NaCl and 10% ethanol either individually or in combination, or basal diet alone for 51 weeks. Further groups of animals were similarly treated with these chemicals without the MNNG pretreatment. All rats were killed at the end of week 52 for histopathological examination. In the forestomach, treatment with catechol alone after MNNG initiation caused a 100% incidence of papillomas (versus 67% in the controls) as well as carcinomas (versus 0% in the controls). On the other hand, the treatment with ethanol alone significantly lowered the incidence of papillomas (13 versus 67% in the controls). The combined treatment with catechol, NaCl and ethanol significantly lowered the incidence of squamous cell carcinomas (57%) as compared to the catechol alone group value (100%). In the glandular stomach, catechol enhanced the development of adenocarcinomas (73 versus 0% in the controls), but this was decreased to 29% by the combined treatment with ethanol and NaCl. NaCl without MNNG pretreatment slightly enhanced epithelial cell proliferation in the forestomach. These results indicate that combined treatment with NaCl and ethanol exerts protective effects against catechol-induced forestomach and glandular stomach carcinogenesis, this apparently being largely due to the ethanol.

Dose-dependent promoting effects of catechol on glandular stomach carcinogenesis in BALB/c mice initiated with N-methyl-N-nitrosourea

The effects of catechol administration in the diet on stomach carcinogenesis in mice after initiation with N-methyl-N-nitrosourea (MNU) in the drinking water were investigated in a development trial for a new experimental protocol. Male 6-week-old BALB/c mice were given MNU in the drinking water intermittently for a total of three one-week periods, with one-week intervals, at the concentration of 120 ppm (groups 1 and 2). Groups 3 and 4 served as non initiated controls. From week 7, groups 1 and 3 were divided into three subgroups and the mice were fed on diet containing 0.05% (groups 1a and 3a), 0.2% (groups 1b and 3b), 08% (groups 1c and 3c) or 0% (groups 2 and 4) catechol for 29 weeks. At week 20, appreciably enhanced development of pepsinogen 1-altered pyloric glands was noted in all catechol-treated groups, in a partially dose-dependent manner (12.8 +/- 12.5, 13.8 +/- 11.7, and 24.0 +/- 12.7/100 pyloric glands respectively, for groups 1, 2 and 3). The incidences of adenomas (groups 1, 2 and 3) were also increased. At week 35, dose-dependent induction of adenocarcinomas in groups 1 (3/19), 2 (3/19) and 3 (14/20) was evident. In addition, the depth of invasion of the adenocarcinomas was enhanced by catechol in a dose-dependent manner, though the histological type was not influenced. Thus, the administration of catechol in the diet strongly enhanced the preneoplastic and neoplastic lesions in mouse glandular stomach induced by MNU in the drinking water, in a dose-dependent manner.

Homogentisic acid and structurally related compounds as intermediates in plasma soluble melanin formation and in tissue toxicities

Homogentisic acid (HGA) spontaneously starts to undergo oxidation and polymerization soon after the beginning of incubation in human blood or plasma at 37 degrees C, and forms plasma soluble melanins (PSM). Haemolysis accompanies this process in blood. The addition of equimolar quantities of antioxidants delays this oxidation significantly (isoascorbic acid by 2:30-4:00 h; glutathione by 3:20-4:05 h; D-penicillamine by 5:00-5:45 h). HGA is a phenylalanine and tyrosine metabolite, related structurally to the catecholamines and other precursors of melanins. HGA is normally metabolized by the enzyme homogentisic acid oxidase. When this enzyme is genetically missing, part of HGA is excreted in the urine, another part polymerizes darkens many tissues (ochronosis), and produces widespread degenerative changes in cartilage and other connective tissues, joints, blood vessels, heart valves, kidneys and in other tissues. Collectively this disorder is known as alcaptonuria, for which no satisfactory treatment is known. The causes of both alcaptonuric arthritis and rheumatoid arthritis are thought to involve increased oxidative stress. Inflammation of joints and connective tissue damage are involved in both diseases. Oxygen radicals are suspected to cause inflammation and cellular damage. Hydroxyl radicals degrade hyaluronic acid (the viscous synovial fluid of joints). High levels of products of free radical reactions, with fluorescence excitation (ex) and emission (em) maxima in the wavelength ranges of those of PSM (ex 320-400 and em 400-470) were reported in the blood sera and synovial fluids of patients with rheumatoid arthritis.(ABSTRACT TRUNCATED AT 250 WORDS)

The beneficial and hazardous effects of simple phenolic compounds

The current emphasis on screening the environment for man-made genotoxic and carcinogenic compounds detracts from studies on the possible health hazard or beneficial effects of naturally occurring agents to which humans are exposed daily. The simple phenolics, which are ubiquitous among plants, used as food additives, and ingested daily in milligram quantities, belong to this category of compounds. They induce double-strand DNA breaks. DNA adducts, mutations and chromosome aberrations in a great variety of test systems. However, they can suppress the genotoxic activity of numerous carcinogenic compounds in both in vitro and in vivo assays. This dual function of dietary phenolics also becomes evident when their carcinogenic or anticarcinogenic potential is examined. Some, but not all, phenolics induce precancerous lesions, papillomas and cancers, act as cocarcinogens, and exert a promoting effect in various rodent assays. On the other hand, phenolics have proved to be potent inhibitors of carcinogenesis at the initiation and promotion stages induced by carcinogens and promoters of different molecular structures. The extent to which a health hazard or protective activity of complex dietary mixtures is due to their phenolic content remains an unresolved issue. In addition, these multiple, occasionally contradictory functions of simple phenolics make it difficult to propose their use as chemopreventive agents.

Para-aminophenol and structurally related compounds as intermediates in lipofuscin formation and in renal and other tissue toxicities

P-aminophenol is considered a minor nephrotoxic metabolite of phenacetin and acetaminophen (paracetamol) in man. Our experiments show that p-aminophenol readily undergoes oxidative polymerization during incubation in human blood or plasma, to form melanin, as a component of soluble lipofuscin. Haemolysis accompanies this process in whole blood. Unmetabolized phenacetin and acetaminophen do not form soluble lipofuscins. Long-term excessive use of phenacetin or acetaminophen has been associated with chronic renal disease, haemolytic anaemia, and increased solid lipofuscin deposition in tissues. Excessive use of phenacetin has also been associated with cancer of renal pelvis and bladder. It appears to us that p-aminophenol and other o- and p-aminophenol metabolites of these drugs are intermediates not only in the etiology of chronic renal disease, but in the other developments as well. P-aminophenol and other ex(end)ogenous aminohydroxyphenyl, aminopolyhydroxyphenyl, polyhydroxyphenyl and polyaminophenyl compounds with these groups in ortho and para positions (such as 3-hydroxyanthranilic acid, 6-aminodopamine, dopamine, p-phenylenediamine, etc.) can undergo autoxidations and metal-catalyzed and enzymatic oxidations in man to produce toxic (semi)quinones(imines), (semi)quinonediimines and reactive oxygen species. After depletion of antioxidants these very reactive (semi)quinones(imines) and (semi)quinonediimine intermediates, many of which are precursors of plasma soluble lipofuscins and melanoproteins, react with essential proteins, DNA, other macromolecules and can cause or contribute to renal and other tissue toxicity, haemolytic anaemia, neoplasia, and granular lipofuscin formation. The reactive oxygen species can also deplete antioxidants, damage essential proteins, DNA, and other macromolecules, and thereby injure cells and extracellular matrix.

Stomach carcinogenicity of caffeic acid, sesamol and catechol in rats and mice

The carcinogenic potential of caffeic acid, sesamol and catechol was examined in male and female F344 rats and B6C3F1 mice, groups of 30 animals being treated with diets containing 2% caffeic acid, 2% sesamol or 0.8% catechol for 104 weeks (rats) or 96 weeks (mice). Histological examination revealed that caffeic acid induced forestomach squamous cell carcinoma in 57% (P less than 0.001 vs. controls) and 50% (P less than 0.001) of male and female rats, respectively, whereas sesamol was associated with squamous cell carcinoma at incidences of 31% (P less than 0.001) in male rats, and 38% (P less than 0.001) and 17% (P less than 0.05) in male and female mice, respectively. Catechol induced glandular stomach adenocarcinomas in 54% (P less than 0.001) and 43% (P less than 0.001) of male and female rats, respectively. The results thus clearly demonstrated that all three antioxidants are carcinogenic in rodent stomach epithelia.

Antioxidants--carcinogenic and chemopreventive properties

Synthetic and naturally occurring antioxidants have a wide variety of biological actions in rodents in addition to their primary antioxidant activity. Some of the included biological effects are of direct interest in relation to studies of carcinogenicity and/or modulation of carcinogenesis. Since the synthetic antioxidant BHA was first found to exert carcinogenic potential in rat and hamster forestomach epithelium, many other synthetic and naturally occurring antioxidants have been examined for their ability to induce proliferative activity in the alimentary canal. These studies have revealed that caffeic acid and sesamol are also tumorigenic for rat forestomach epithelium, whereas catechol and p-methylcatechol induce neoplasia in rat glandular stomach epithelium. Although the proliferative response is very rapid, with inflammation and ulceration, it takes a very long time before carcinomas develop. The proliferative lesions in the forestomach induced by BHA or caffeic acid are largely reversible, in contrast to those induced by genotoxic carcinogens, which generally persist and develop into cancer. Therefore, chronic irritation is considered to be responsible for the induction of stomach cancer by antioxidants. Butylated hydroxyanisole can undergo oxidative metabolism in vitro, and some of the metabolites formed have the potential for binding to proteins. Neither BHA nor its metabolites binds to DNA in vivo, but protein binding in the forestomach was greater than 10 times higher than that in the glandular stomach. It is thus conceivable that BHA is oxidatively metabolized in the forestomach epithelium (possibly entering into redox cycling), and reactive metabolites including semiquinone radicals or active oxygen species are responsible for the carcinogenesis by a mechanism involving binding to macromolecules. Many antioxidants have been shown to modify carcinogenesis, and as a rule, they inhibit the initiation stage by reducing the interaction between carcinogen and DNA. However, both promotion and inhibition have been reported for second-stage carcinogenesis, depending on the organ site, species of animal, or initiating carcinogen. They can also block reaction of amine and nitrite to form nitrosamines or reduce TPA promotion of skin carcinogenesis. Generally high doses of antioxidants are required for carcinoma induction or modification of chemical carcinogenesis. The significance of the reported tumorigenicity and strong promoting activity of antioxidants for forestomach epithelium of animals to the development of human cancer appears limited mainly because humans do not have a forestomach. The carcinogenic and strong promoting activities of catechol and its structurally related compounds on rat glandular stomach epithelium are of greater concern because this tissue is directly analogous to human gastric epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Elevated levels of plasma lipofuscins in patients with chronic renal failure

The fluorescence excitation and emission spectra observed in plasma from patients with chronic renal failure were reproduced by the generation of soluble lipofuscins in normal plasma samples by incubation with mixtures of L-dopa, dopamine, L-norepinephrine, L-epinephrine, 3-hydroxy-DL-kynurenine and 3-hydroxy-anthranilic acid for 24 h at 37 degrees C. Relative fluorescence intensity measurements consistently showed elevated plasma levels of the soluble lipofuscins in chronic renal failure: the means (n = 27) were 73.9 +/- 33.4 (SD) and 71.1 +/- 14.8 at emissions 413 nm and 445 nm respectively, in contrast to those of normal plasma samples (n = 11), 18.2 +/- 5.3 and 23.1 +/- 5.6. The maximum or shoulder at approximately 413 nm represents soluble lipofuscin that can be generated from 3-hydroxyanthranilic acid and the maximum or shoulder at approximately 445 nm represents soluble lipofuscins derived from the precursors listed above and probably from other related precursors. Gravimetric measurements also showed elevated levels of melanins in the plasma samples of patients with chronic renal failure: 2.72 +/- 0.38 mg/ml (n = 16), as compared to normal values: 1.70 +/- 0.10 mg/ml (n = 6). In individual patients haemodialysis reduced the fluorescence intensities to a range of 65-99% and the melanin levels to a range of 86-99% of the pre-dialysis values.

Dietary carcinogens and anticarcinogens. Oxygen radicals and degenerative diseases

The human diet contains a great variety of natural mutagens and carcinogens, as well as many natural antimutagens and anticarcinogens. Many of these mutagens and carcinogens may act through the generation of oxygen radicals. Oxygen radicals may also play a major role as endogenous initiators of degenerative processes, such as DNA damage and mutation (and promotion), that may be related to cancer, heart disease, and aging. Dietary intake of natural antioxidants could be an important aspect of the body's defense mechanism against these agents. Many antioxidants are being identified as anticarcinogens. Characterizing and optimizing such defense systems may be an important part of a strategy of minimizing cancer and other age-related diseases.