In soil, fertilizers containing inorganic nitrogen and wastes containing organic nitrogen are first decomposed to give ammonia, which is then oxidized to nitrite and nitrate. The nitrate is taken up by plants during their growth and used in the synthesis of organic nitrogenous compounds. Surplus nitrate readily moves with groundwater (2, 3). Under aerobic conditions, it percolates in large quantities into the aquifer because of the small extent to which degradation or denitrification occurs. Under anaerobic conditions, nitrate may be denitrified or degraded almost completely to nitrogen. The presence of high or low water tables, the amount of rainwater, the presence of other organic material, and other physicochemical properties are also important in determining the fate of nitrate in soil ( 4). In surface water, nitrification and denitrification may also occur, depending on the temperature and pH. The uptake of nitrate by plants, however, is responsible for most of the nitrate reduction in surface water. Nitrogen compounds are formed in the air by lightning or discharged into it from industrial processes, motor vehicles, and intensive agriculture. Nitrate is present in air primarily as nitric acid and inorganic aerosols, as well as nitrate radicals and organic gases or aerosols. These are removed by wet and dry deposition.

WHO guidelines for drinking-water quality.

The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.

The immunobiology of cancer immunosurveillance and immunoediting

The biochemistry and medical significance of the flavonoids.

The emergence of tissue engineering raises new possibilities for the study of complex physiological and pathophysiological processes in vitro. Many tools are now available to create 3D tissue models in vitro, but the blueprints for what to make have been slower to arrive. We discuss here some of the 'design principles' for recreating the interwoven set of biochemical and mechanical cues in the cellular microenvironment, and the methods for implementing them. We emphasize applications that involve epithelial tissues for which 3D models could explain mechanisms of disease or aid in drug development.

Capturing complex 3D tissue physiology in vitro.

Discrimination of active metabolites of amino stilbenes as mutagens

Two forms of human liver cytosolic epoxide hydrolase (cEH) with diagnostic substrate specificity for trans-stilbene oxide (cEHTSO) and cis-stilbene oxide (cEHCSO) have been identified, and cEHCSO was purified to apparent homogeneity. The enzyme had a monomer molecular weight of 49 kDa and an isoelectric point of 9.2. Pure cEHCSO hydrolyzed CSO at a rate of 145 nmole/min/mg. TSO was not metabolized at a detectable level, and like cEHTSO, the enzyme was about three times more active at pH 7.4 than at pH 9.0. Unlike cEHTSO, cEHCSO was efficiently inhibited by 1 mM 1-trichloropropene oxide (90.5%) and 1 mM STO (92%). Similarly, liver cEH purified 541-fold from fenofibrate induced Fischer 344 rats was shown to be a native 120 kDa dimer of two 61 kDa subunits. The enzyme expressed maximum activity of 205 nmole/min/mg at pH 7.4 toward the diagnostic substrate TSO with an apparent Km of 1.7 microM. In Western blots, polyclonal antibodies against rat liver cEH were shown to recognize a single 61 kDa protein band from liver cytosol of rat, mouse, guinea pig, Syrian hamster, and rabbit. This antibody precipitated neither human liver cEHTSO or cEHCSO. Antibodies against rat liver microsomal epoxide hydrolase reacted with cEHCSO in the Western blot and on immunoprecipitation. Using antibodies against rat liver cEH, 24 positive clones were picked upon colony blot screening of a pEX 1/E. coli POP 2136 expression library.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.

Dibenz[a,h]anthracene (DB[a,h]A) and the related 3,4-diol and anti- and syn-3,4-diol 1,2-oxides were applied to the shaved dorsal skin of groups of four C57Bl/CB1 mice Twenty-four hours later the mice were killed, DNA isolated from the treated skin, hydrolysed and examined for the presence of aromatic adducts using the nuclease P1 modification of the 32P-postlabelling technique Autoradiography of the maps obtained by chromatography on polyethyleneimine-cellulose plates showed that six DNA adduct spots that were derived from DB[a,h]A were also present in the DNA of skin treated with the DBA 3,4-diol and that, whilst four of these adduct spots were also seen in maps prepared from the DNA of skin treated with the anti-3,4-diol-1,2-oxide, they were not present in DNA from skin to which the syn-isomer had been applied The identity of these adduct spots was confirmed by their coincidence when mixtures of different DNA hydrolysates were chromatographed together Quantitatively, the highest levels of mouse skin modification were obtained with the diol-epoxides and the lowest with DB[a,h]A The results suggest that most of the DNA adducts formed in DB[a,h]A-treated mouse skin arise through metabolism of the hydrocarbon to the related 3,4-diol and that some may be formed following the conversion of this diol to the bay-region anti-3,4-diol-1,2-oxide

The metabolic activation of dibenz[a,h]anthracene in mouse skin examined by 32P-postlabelling: minor contribution of the 3,4-diol 1,2-oxides to DNA binding.

The metabolic activation of dibenz[a,h]anthracene in mouse skin examined by 32P-postlabelling

Agroclavine, an alkaloid produced by some species of fungi and dicotyledon plants, and its 1-alkylated derivatives are potentially useful as antineoplastic drugs, since they exert potent and selective cytostatic effects. In the present study, we have investigated agroclavine and its 1-propyl and 1-pentyl derivatives for mutagenicity. The genetic end point studied was the reversion of strains of Salmonella typhimurium (TA 100, TA 98, TA 1537) and Escherichia coli (WP2. uvrA ), auxotrophic for histidine and tryptophan, respectively. The compounds were tested directly and in the presence of a mammalian xenobiotic-metabolizing system. In the direct test, agroclavine and the two alkylated derivatives examined exhibited substantial bacteriotoxicity but no mutagenicity. Addition of NADPH-fortified postmitochondrial supernatant fraction of rat liver homogenate led to a clear-cut decrease in bacteriotoxicity and to the formation of mutagenic products. Each compound was effective in all three strains of S. typhimurium used. In E. coli only spurious effects were seen. 1-Pentylagroclavine, the most hydrophobic compound in the series, was the strongest mutagen. Agroclavine, the least hydrophobic compound, was the weakest. The mutagenic potencies and efficacies of all these test compounds were much weaker than those of the positive controls, which were known mutagens and carcinogens. Moreover, the differential effect of metabolism by liver enzymes demonstrates that the toxicity and mutagenicity of agroclavine and its derivatives are caused by different chemical species. Hence, it may be possible to develop derivatives that are cytotoxic but not mutagenic.

Franz Oesch

Papers

Discrimination of active metabolites of amino stilbenes as mutagens

Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.

The metabolic activation of dibenz[a,h]anthracene in mouse skin examined by 32P-postlabelling: minor contribution of the 3,4-diol 1,2-oxides to DNA binding.

The metabolic activation of dibenz[a,h]anthracene in mouse skin examined by 32P-postlabelling

Mutagenicity Experiments on Agroclavines, New Natural Antineoplastic Compounds