Immunoassay for single-stranded DNA in apoptotic cells

The apoptosis assay described in this chapter is based on the selective denaturation of DNA in condensed chromatin of apoptotic cells and the detection of denatured DNA with a monoclonal antibody highly specific to single-stranded DNA. Optimal results are obtained by the heating at a relatively low temperature in the presence of formamide. The assay detects apoptotic cells but not necrotic cells or cells with DNA breaks in the absence of apoptosis. The sensitivity of the assay reflects the detection of early and late apoptosis. Apoptotic cells are detected in the sections of frozen or formalin-fixed paraffin-embedded tissues by immunohistochemistry and in the cell suspensions by flow cytometry or fluorescence microscopy. Apoptosis enzyme-linked immunoassay based on DNA denaturation by formamide in microtiter plates and one-step immunostaining is applied for high-throughput screening of drugs. The enzyme-linked immunoassay has the ability to distinguish anticancer drugs from toxic chemicals, to predict selective toxicity to cancer cells, and to detect drug synergism.

Structure of Three Class I Human Alcohol Dehydrogenases Complexed with Isoenzyme Specific Formamide Inhibitors,

Formamides are aldehyde analogues that have demonstrated potent and selective inhibition of human alcohol dehydrogenase isoenzymes. The alphaalpha, beta(1)beta(1), gamma(2)gamma(2), and sigmasigma isoforms have all been found to be strongly inhibited by substituted formamides. In this paper, the structure of the alphaalpha isoform of human alcohol dehydrogenase complexed with N-cyclopentyl-N-cyclobutylformamide was determined by X-ray crystallography to 2.5 A resolution, the beta(1)beta(1) isoform of human alcohol dehydrogenase complexed with N-benzylformamide and with N-heptylformamide was determined to 1.6 and 1.65 A resolution, respectively, and the structure of the gamma(2)gamma(2) isoform complexed with N-1-methylheptylformamide was determined to 1.45 A resolution. These structures provide the first substrate-level view of the local structural differences that give rise to the individual substrate preferences shown by these highly related isoenzymes. Consistent with previous work, the carbonyl oxygen of the inhibitors interacts directly with the catalytic zinc and the hydroxyl group of Thr48 (Ser48 for gamma(2)gamma(2)) of the enzyme. The benzene ring of N-benzylformamide and the carbon chains of N-heptylformamide and N-1-methylheptylformamide interact with the sides of the hydrophobic substrate pocket whose size and shape is dictated by residue exchanges between the beta(1)beta(1) and gamma(2)gamma(2) isoenzymes. In particular, the exchange of Ser for Thr at position 48 and the exchange of Val for Leu at position 141 in the gamma(2)gamma(2) isoenzyme create an environment with stereoselectivity for the R-enantiomer of the branched N-1-methylheptylformamide inhibitor in this isoenzyme. The primary feature of the alphaalpha isoform is the Ala for Phe93 exchange that enlarges the active site near the catalytic zinc and creates the specificity for the branched N-cyclopentyl-N-cyclobutylformamide inhibitor, which shows the greatest selectivity for this unique isoenzyme of any of the formamide inhibitors.

Analysis of metabolites of N,N-dimethylformamide in urine samples

AIM

To assess the suitability of different methods for biological monitoring of internal dose to N,N-dimethylformamide (DMF) in occupational settings.

METHODS

The determination of urinary metabolites of DMF, N-hydroxymethyl- N-methylformamide (HMMF), N-methylformamide (NMF) and N-acetyl- S-(N-methylcarbamoyl) cysteine (AMCC) was carried out by four selected analytical procedures. Two methods solely measured total NMF (HMMF and NMF). The other two methods measured both total NMF and AMCC in one analytical run. All four methods were tested on 34 urine samples from workers exposed to DMF.

RESULTS

Comparison of the four methods for determination of total NMF in urine showed that results were similar for three methods, while the remaining one provided NMF levels significantly lower (by 22%) than the other methods. Thus, all but one of the tested methods for the determination of total NMF can be considered to be suitable for biological monitoring of internal dose to DMF. The two tested methods for the determination of AMCC afforded results that showed high correlation but differed significantly (by 10%).

CONCLUSION

The choice of the biomonitoring method depends mainly on the purpose for which the measurement is conducted. For evaluation of acute exposures or to assess safety measures in the working area, an updated version of the traditional method of Kimmerle and Eben (1975a, b) for the determination of total NMF in urine is sufficient. For risk assessment after exposure to DMF, the determination of AMCC should be carried out, since AMCC, but not total NMF, is supposed to be related to the toxicity of DMF. However, there is still a need to develop an easier, more sensitive and more selective method for the determination of AMCC in urine until AMCC can be considered for regulatory purposes in occupational settings.

Sperm function in workers exposed to N,N-dimethylformamide in the synthetic leather industry

OBJECTIVE

To determine whether occupational exposure to N,N-dimethylformamide (DMF) for men has adverse effects on sperm function.

DESIGN

Cross-sectional study.

SETTING

A synthetic leather factory in Taiwan.

PATIENT(S)

Twelve DMF-exposed workers in a synthetic leather factory and 8 socioeconomically matched control workers from another non-DMF-exposed manufacturing plant in the vicinity were recruited.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Breathing-zone monitoring of DMF exposure covering the full work shift was implemented on each participant. Urine specimens were collected from each worker immediately after their work shift in parallel with environmental sampling. Environmental DMF and urinary N-methylformamide (NMF) levels were measured by gas chromatograph. Analysis of semen samples was performed to measure semen volume, sperm concentration, morphology, and motility in accordance with World Health Organization criteria.

RESULT(S)

Both conventional microscopy and computer-assisted semen analysis showed that sperm motility in DMF-exposed group was significantly reduced from that in controls. Motility parameters were related to urinary NMF in a dose-response manner but were not related to airborne DMF.

CONCLUSION(S)

Workers occupationally exposed to DMF could be at risk of sperm motility perturbation. The responsible toxicant for the alterations of sperm function could be the active NMF metabolite instead of DMF, but this conclusion warrants a further complete investigation.

The nuclear actin-related protein Act3p/Arp4p of Saccharomyces cerevisiae is involved in transcription regulation of stress genes

A mutational analysis of the essential nuclear actin-related protein of Saccharomyces cerevisiae, Act3p/Arp4p, was performed. The five residues chosen for substitution were amino acids conserved between actin and Act3p/Arp4p, the tertiary structure of which most probably resembles that of actin. Two thermosensitive (ts) mutants, a single and a double point mutant, and one lethal double point mutant were obtained. Both ts mutants were formamide-sensitive which supports a structural relatedness of Act3p/Arp4p to actin; they were also hypersensitive against hydroxyurea and ultraviolet irradiation pointing to a possible role of Act3p/Arp4p in DNA replication and repair. Their 'suppressor of Ty' (SPT) phenotype, observed with another ts mutant of Act3p/Arp4p before, suggested involvement of Act3p/Arp4p in transcription regulation. Accordingly, genome-wide expression profiling revealed misregulated transcription in a ts mutant of a number of genes, among which increased expression of various stress-responsive genes (many of them requiring Msn2p/Msn4p for induction) was the most salient result. This provides an explanation for the mutant's enhanced resistance to severe thermal and oxidative stress. Thus, Act3p/Arp4p takes an important part in the repression of stress-induced genes under non-stress conditions.

Repair of DNA containing Fapy.dG and its beta-C-nucleoside analogue by formamidopyrimidine DNA glycosylase and MutY

Fapy.dG is produced in DNA as a result of oxidative stress. Under some conditions Fapy.dG is formed in greater yields than 8-oxodG from a common chemical precursor. Recently, Fapy.dG and its C-nucleoside analogue were incorporated in chemically synthesized oligonucleotides at defined sites. Like 8-oxodG, Fapy.dG instructs DNA polymerase to misincorporate dA opposite it in vitro. The interactions of DNA containing Fapy.dG or the nonhydrolyzable analogue with Fpg and MutY are described. Fpg excises Fapy.dG (K(M) = 2.0 nM, k(cat) = 0.14 min(-1)) opposite dC approximately 17-fold more efficiently than when mispaired with dA, which is misinserted by DNA polymerase in vitro. Fpg also prefers to bind duplexes containing Fapy.dG.dC or beta-C-Fapy.dG.dC compared to those in which the lesion is opposite dA. MutY incises dA when it is opposite Fapy.dG and strongly binds duplexes containing the lesion or beta-C-Fapy.dG. Incision from Fapy.dG.dA is faster than from dG.dA mispairs but slower than from DNA containing 8-oxodG opposite dA. These data demonstrate that Fapy.dG closely resembles the interactions of 8-oxodG with two members of the GO repair pathway in vitro. The similar effects of Fapy.dG and 8-oxodG on DNA polymerase and repair enzymes in vitro raise the question as to whether Fapy.dG elicits similar effects in vivo.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 2: 8-formamidocyclazocine analogues

High affinity binding for mu and kappa opioid receptors has been observed in analogues of cyclazocine, ethylketocyclazocine and naltrexone where the prototypic (of opiates) phenolic OH group was replaced with a formamide (-NHCHO) group. For the 8-formamide analogue of cyclazocine, binding is highly enantiospecific (eudismic ratios approximately 2000 for mu and kappa) with K(i) values </=1 nM observed for the (2R,6R,11R)-isomer, (-)-4. A preliminary SAR revealed that affinity is very sensitive to substitution on the formamide appendage.

New beta-adrenergic agonists used illicitly as growth promoters in animal breeding: chemical and pharmacodynamic studies

Clenbuterol and beta-adrenergic receptor agonist drugs are illegally used as growth promoters in animal production. Pharmacologically active residues in edible tissues led to intoxication outbreaks in several countries. Pressure of official controls pulsed synthesis of new compounds to escape analytical procedures. We report two new compounds named 'A' and 'G4', found in feeding stuffs. Chemical structure was studied through nuclear magnetic resonance-imaging and infrared spectroscopy, and beta(1)- and beta(2)-adrenergic activity was evaluated on isolated guinea-pig atrium and trachea in comparison with clenbuterol. Both compounds share with clenbuterol an halogenated aromatic ring with a primary amino group. Main modifications consisted of substitution of secondary amino group with an alkyl chain in compound A and substitution of the ter-butyl group with a benzene ring in compound G4. In guinea-pig trachea these compounds showed myorelaxant potency lower than clenbuterol (EC(50) was 43.8 nM for clenbuterol, 11700 nM for compound A, 2140 nM for G4). On the contrary, in the guinea-pig atrium (heart-beat rate stimulant effect) the compounds were more potent than clenbuterol (EC(50) was 15.2 nM for clenbuterol, 3.4 nM for compound A, 2.8 nM for G4). These pharmacodynamic properties, and stronger lipophilic properties shown by the two compounds may result in increased cardiovascular risk for consumers of illicitly treated animals.

Deacylation of N-arylformamides and N-arylacetamides by formamidase in rat liver

The in vitro deacylation of N-arylformamides and N-arylacetamides to arylamines was examined in rat liver preparations. When 2-acetylaminofluorene or 2-formylaminofluorene was incubated with rat liver microsomes or cytosol, the deacylated metabolite, 2-aminofluorene, was formed. The deacylating activity of liver microsomes was inhibited by bis(4-nitrophenyl)phosphate and phenylmethanesulfonyl fluoride, inhibitors of carboxylesterase. In contrast, the activity of liver cytosol was inhibited by diisopropyl fluorophosphate, an inhibitor of formamidase. Deacylation of these compounds appear to be mainly catalyzed by carboxylesterase in liver microsomes and formamidase in liver cytosol. 2-Formylaminofluorene, 2-acetylaminofluorene, 1-formylaminopyrene, 4-formylaminobiphenyl, 2-formylaminonaphthalene, 1-formylaminonaphthalene, and 2-acetylaminofluorene were deacylated by formamidase purified from rat liver cytosol. Formamidase catalyzed both N-formylation of arylamines, and deacylation of N-arylformamides and N-arylacetamides.

Clinical pharmacokinetics, pharmacodynamics and metabolism of the novel matrix metalloproteinase inhibitor ABT-518

PURPOSE

To investigate the pharmacokinetics, pharmacodynamics and metabolism of the novel matrix metalloproteinase (MMP) inhibitor ABT-518.

METHODS

Plasma and urine samples were obtained from six patients included in a phase I trial in which ABT-518 was given once daily via the oral route. Samples were analyzed by LC-MS/MS, ELISA and immunocapture assay. The pharmacokinetics of the parent compound and of detectable metabolites were calculated.

RESULTS

After a single dose of ABT-518 peak plasma levels were reached within 4-8 h. ABT-518 had an estimated clearance (Cl/F) of approximately 3 l/h, an estimated volume of distribution (V/F) of over 70 l and a terminal half-life (T(1/2)) of 20 h. At least six different metabolites were formed. Pharmacodynamic analysis for angiogenic growth factors (bFGF and VEGF) showed plasma and urine levels in the picogram range and for total MMP-9 and MMP-2 or MMP-9 activity showed plasma and urine levels in the nanogram range.

CONCLUSIONS

The MMP inhibitor ABT-518 is extensively metabolized in humans. No significant correlations between pharmacokinetics and pharmacodynamics could be established.

Fapy.dG instructs Klenow exo(-) to misincorporate deoxyadenosine

The effects of Fapy.dG (N-(2-deoxy-alpha,beta-d-erythropentofuranosyl)-N-(2,6-diamino-4-hydroxy-5-formamidopyrimidine)) on the activity of Klenow exo- have been determined by using oligonucleotide substrates containing the lesion at a defined site. Fapy.dG inhibits primer polymerization at two positions: nucleotide incorporation opposite the lesion and extension one nucleotide past the lesion. Klenow exo- is inhibited less by Fapy.dG than by its analogue, MeFapy.dG. Fapy.dG instructs the polymerase to misincorporate deoxyadenosine opposite itself 20 times more frequently than does dG. Extension of the primer containing the Fapy.dG:dA base pair is only slightly less efficient than when dC is opposite the lesion. Overall, Fapy.dG increases the probability that Klenow exo- will make a mistake during replication approximately 80-million fold compared to a template containing the native nucleotide, dG.

Hydroxylation of deoxyguanosine at 5' site of GG and GGG sequences in double-stranded DNA induced by carbamoyl radicals

Free radicals generated by chemicals can cause sequence-specific DNA damage and play important roles in mutagenesis and carcinogenesis. Carbamoyl group (CONH2) and its derived groups (CONR2) occur as natural products and synthetic chemical compounds. We have investigated the DNA damage by carbamoyl radicals .(CONH2), one of carbon-centered radicals. Electron spin resonance (ESR) spectroscopic study has demonstrated that carbamoyl radicals were generated from formamide by treatment with H2O2 plus Cu(II), and from azodicarbonamide by treatment with Cu(II). We have investigated sequence specificity of DNA damage induced by carbamoyl radicals using 32P-labeled DNA fragments obtained from the human c-Ha-ras-1 and p53 genes. Treatment of double-stranded DNA with carbamoyl radicals induced an alteration of guanine residues, and subsequent treatment with piperidine or Fpg protein led to chain cleavages at 5'-G of GG and GGG sequences. Carbamoyl radicals enhanced Cu(II)/H2O2-mediated formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in double-stranded DNA more efficiently than that in single-stranded DNA. These results shows that carbamoyl radicals specifically induced hydroxylation of deoxyguanosine at 5' site of GG and GGG sequences in double-stranded DNA.

Influence of a terminal formamido group on the sequence recognition of DNA by polyamides

Pyrrole (Py)-imidazole (Im)-containing polyamides bind in the minor groove of DNA and can recognize specific sequences through a stacked antiparallel dimer. It has been proposed that there are two different low energy ways to form the stacked dimer and that these are sensitive to the presence of a terminal formamido group: (i) a fully overlapped stacking mode in which the N-terminal heterocycles of the dimer stack on the amide groups between the two heterocycles at the C-terminal and (ii) a staggered stacking mode in which the N-terminal heterocycles are shifted by approximately one unit in the C-terminal direction (Structure 1997, 5, 1033-1046). Two different DNA sequences will be recognized by the same polyamide stacked in these two different modes. Despite the importance of polyamides as sequence specific DNA recognition agents, these stacking possibilities have not been systematically explored. As part of a program to develop agents that can recognize mismatched base pairs in DNA, a set of four polyamide trimers with and without terminal formamido groups was synthesized, and their interactions with predicted DNA recognition sequences in the two different stacking modes were evaluated. Experimental difficulties in monitoring DNA complex formation with polyamides were overcome by using surface plasmon resonance (SPR) detection of the binding to immobilized DNA hairpin duplexes. Both equilibrium and kinetic results from SPR show that a terminal formamido group has a pronounced effect on the affinity, sequence specificity, and rates of DNA-dimer complex formation. The formamido polyamides bind preferentially in the staggered stacking mode, while the unsubstituted analogues bind in the overlapped mode. Affinities for cognate DNA sequences increase by a factor of around 100 when a terminal formamido is added to a polyamide, and the preferred sequences recognized are also different. Both the association and the dissociation rates are slower for the formamido derivatives, but the effect is larger for the dissociation kinetics. The formamido group thus strongly affects the interaction of polyamides with DNA and changes the preferred DNA sequences that are recognized by a specific polyamide stacked dimer.

Substrate-regulated cyanide hydratase (chy) gene expression in Fusarium solani: the potential of a transcription-based assay for monitoring the biotransformation of cyanide complexes

The fungus Fusarium solani detoxifies cyanide through induction of the cyanide hydratase gene activity (chy) in the presence of either KCN or the metal-complexed cyanides, K2Ni(CN)4 or K4Fe(CN)6, at pH 7.0 and 4.0 respectively. Sequence analysis of the chy gene identified primers for reverse transcriptase-polymerase chain reaction (RT-PCR)-directed analysis of mRNA transcripts, which demonstrated that activity correlated to the substrate-specific induction of gene expression. chy transcription was initiated 30-60 min after exposure of F. solani cultures to cyanide complexes. Maximum expression was detected within 4.5 h, after which chy mRNA synthesis declined below the limits of detection within 26 h. A lag period of approximately 2 h, following initial transcription, was recorded before cyanide complexes were converted to formamide. mRNA transcripts of chy were not detected in the absence of cyanide or cyanide complexes. The presence of introns within the gene resulted in a difference in size of 100 bp for DNA compared with mRNA of the corresponding 5' region. This size difference facilitated PCR detection of gene and transcript respectively. Comparisons of the predicted amino acid sequence of the F. solani chy gene and those of Gloeocerospora sorghi, Fusarium lateritium and Leptosphaeria maculans demonstrate that cyanide hydratase genes are highly conserved and of a similar evolutionary origin. These data predict that the functional assay described here to monitor the induction of chy gene expression and, potentially, cyanide degradation would be applicable to a variety of polluted environments.

Analysis of two matrix metalloproteinase inhibitors and their metabolites for induction of phospholipidosis in rat and human hepatocytes(1)

ABT-770 [(S)-N-[1-[[4'-trifluoromethoxy-[1,1'-biphenyl]-4-yl]oxy]methyl-2-(4,4-dimethyl-2,5-dioxo-1-imidazolidinyl)ethyl]-N-hydroxyformamide], a matrix metalloproteinase inhibitor (MMPI), produced generalized phospholipidosis in rats. Phospholipid accumulation was accompanied by retention of drug-related material and was associated with increased mortality. Generation of a successful drug candidate depended upon understanding the cause of the phospholipidosis and redesigning the chemical structure accordingly. ABT-770 and other MMPIs, plus several metabolites of each, were assayed for their ability to induce phospholipidosis in primary cultured rat and human hepatocytes. Phospholipid accumulation was detected by following the incorporation of a fluorescent phospholipid analogue into intracytoplasmic inclusion bodies characteristic of phospholipid storage disorders. At 24 and 48 hr, none of the parent compounds induced phospholipidosis in vitro in rat or human hepatocytes. Phospholipidosis was associated primarily with an amine metabolite of ABT-770. The amine metabolite of another MMPI, ABT-518 ([S-(R*,R*)]-N-[1-(2,2-dimethyl-1,3-dioxol-4-yl)-2-[[4-[4-(trifluoromethoxy)-phenoxy]phenyl]sulfonyl]ethyl]-N-hydroxyformamide), produced little phospholipidosis in rat and human hepatocytes even at concentrations up to 100 microM. The presence or absence of phospholipidosis in the in vitro assay correlated well with ultrastructural findings and drug accumulation in rat tissues. ABT-770, which produced phospholipidosis associated with its amine metabolite in vitro and in vivo, also generated a higher tissue to plasma distribution of metabolites particularly in tissues where phospholipidosis was observed. ABT-518 and its amine metabolite, however, produced low tissue to plasma ratios and induced little to no phospholipidosis in vitro or in vivo. These results demonstrate that the phospholipidosis observed for ABT-770 could be attributed to a cationic metabolite, and that altering the properties of such a metabolite, by modification of the parent compound, alleviated the disorder.

Insertion polymorphism of CYP2E1 and urinary N-methylformamide after N,N- dimethylformamide exposure in Japanese workers

OBJECTIVES

This study examined whether consideration of the *1C/*1D CYP2E1 insertion polymorphism is important for interpreting the biological monitoring of exposure to N,N-dimethylformamide (DMF) in Japanese workers.

METHODS

The insertion genotype, airborne DMF exposure on the last day of a work week, and NMF in urine sampled just after the last workshift of the week were determined in 44 male and female Japanese workers.

RESULTS AND CONCLUSIONS

The allelic frequency of this CYP2E1 polymorphism was 0.261 in this Japanese population of workers. The CYP2E1 insertion polymorphism did not contribute to NMF levels even after consideration of BMI or alcohol intake. The results indicate that CYP2E1 insertion polymorphism does not appear to be an important determinant for the interpretation of biological exposure to DMF by the measurement of urinary NMF.

Discovery of a novel enzyme, isonitrile hydratase, involved in nitrogen-carbon triple bond cleavage

Isonitrile containing an N triple bond C triple bond was degraded by microorganism sp. N19-2, which was isolated from soil through a 2-month acclimatization culture in the presence of this compound. The isonitrile-degrading microorganism was identified as Pseudomonas putida. The microbial degradation was found to proceed through an enzymatic reaction, the isonitrile being hydrated to the corresponding N-substituted formamide. The enzyme, named isonitrile hydratase, was purified and characterized. The native enzyme had a molecular mass of about 59 kDa and consisted of two identical subunits. The enzyme stoichiometrically catalyzed the hydration of cyclohexyl isocyanide (an isonitrile) to N-cyclohexylformamide, but no formation of other compounds was detected. The apparent K(m) value for cyclohexyl isocyanide was 16.2 mm. Although the enzyme acted on various isonitriles, no nitriles or amides were accepted as substrates.

The formamidase gene of Aspergillus nidulans: regulation by nitrogen metabolite repression and transcriptional interference by an overlapping upstream gene

The ability to utilize formamide as a sole nitrogen source has been found in numerous fungi. We have cloned the fmdS gene encoding a formamidase from Aspergillus nidulans and found that it belongs to a highly conserved family of proteins separate from the major amidase families. The expression of fmdS is primarily regulated via AreA-mediated nitrogen metabolite repression and does not require the addition of exogenous inducer. Consistent with this, deletion analysis of the 5' region of fmdS has confirmed the presence of multiple AreA-binding sites containing a characteristic core GATA sequence. Under carbon starvation conditions the response to nitrogen starvation is eliminated, indicating that the lack of a carbon source may result in inactivation of AreA. Sequence analysis and isolation of cDNAs show that a gene of unknown function lies directly 5' of fmdS with its transcript overlapping the fmdS coding region. Disruption of the 5' gene and analysis of the effects of overexpression of this gene on fmdS expression has shown that expression of this upstream gene interferes with fmdS transcription, resulting in a strong dependence on AreA activation for expression. Therefore the relative position of these two genes is essential for normal regulation of fmdS.

Crystal structures of mouse class II alcohol dehydrogenase reveal determinants of substrate specificity and catalytic efficiency

The structure of mouse class II alcohol dehydrogenase (ADH2) has been determined in a binary complex with the coenzyme NADH and in a ternary complex with both NADH and the inhibitor N-cyclohexylformamide to 2.2 A and 2.1 A resolution, respectively. The ADH2 dimer is asymmetric in the crystal with different orientations of the catalytic domains relative to the coenzyme-binding domains in the two subunits, resulting in a slightly different closure of the active-site cleft. Both conformations are about half way between the open apo structure and the closed holo structure of horse ADH1, thus resembling that of ADH3. The semi-open conformation and structural differences around the active-site cleft contribute to a substantially different substrate-binding pocket architecture as compared to other classes of alcohol dehydrogenase, and provide the structural basis for recognition and selectivity of alcohols and quinones. The active-site cleft is more voluminous than that of ADH1 but not as open and funnel-shaped as that of ADH3. The loop with residues 296-301 from the coenzyme-binding domain is short, thus opening up the pocket towards the coenzyme. On the opposite side, the loop with residues 114-121 stretches out over the inter-domain cleft. A cavity is formed below this loop and adds an appendix to the substrate-binding pocket. Asp301 is positioned at the entrance of the pocket and may control the binding of omega-hydroxy fatty acids, which act as inhibitors rather than substrates. Mouse ADH2 is known as an inefficient ADH with a slow hydrogen-transfer step. By replacing Pro47 with His, the alcohol dehydrogenase activity is restored. Here, the structure of this P47H mutant was determined in complex with NADH to 2.5 A resolution. His47 is suitably positioned to act as a catalytic base in the deprotonation of the substrate. Moreover, in the more closed subunit, the coenzyme is allowed a position closer to the catalytic zinc. This is consistent with hydrogen transfer from an alcoholate intermediate where the Pro/His replacement focuses on the function of the enzyme.

Biological monitoring of occupational exposure to N,N-dimethylformamide--the effects of co-exposure to toluene or dermal exposure

OBJECTIVES

The objective of this study is to assess the exposure and intake dose of N,N-dimethylformamide (DMF) and the correlation between them, according to the type of exposure for the workers in the DMF industry.

METHODS

We monitored 345 workers occupationally exposed to DMF, from 15 workshops in the synthetic fiber, fiber coating, synthetic leather and paint manufacturing industries. Ambient monitoring was carried out with personal samplers to monitor the external exposure. Biological monitoring was done to determine the internal dose by analyzing N-methylformamide (NMF) in end-shift urine. Work procedure and exposure type of each DMF workshop was carefully surveyed, to classify workers by exposure type according to work details. Workers were classified into three groups (Group A: continuous and direct exposure through inhalation and skin; Group B: intermittent and short-term exposure through inhalation and skin; Group C: continuous and indirect exposure mostly through inhalation).

RESULTS

Geometric mean of DMF concentration in air was 2.62 (GSD 5.30) ppm and that of NMF in urine was 14.50 (GSD 3.89) mg/l. In the case of continuous absorption through inhalation and dermal exposure (Group A), the value of NMF in urine corresponding to 10 ppm of DMF was 45.3 mg/l (r = 0.524, n = 178), 39.1 mg/g creatinine (r = 0.424), while it was 37.7 mg/l (r = 0.788, n = 37), 24.2 mg/g creatinine (r = 0.743) in the case of absorption mostly through inhalation (Group C). Creatinine correction reduced the correlation between two parameters.

CONCLUSION

The NMF in urine corresponding to 10 ppm DMF, of the dermal and inhalation exposure group was 39.1 mg/g creatinine (r = 0.424, n = 178), while that of the inhalation exposure-only group was 24.2 mg/g creatinine (r = 0.743, n = 37). Co-exposure with toluene reduced the NMF excretion in urine.

Evaluation of dynamic polar molecular surface area as predictor of drug absorption: comparison with other computational and experimental predictors

The relationship between various molecular descriptors and transport of drugs across the intestinal epithelium was evaluated. The monolayer permeability (Pc) of human intestinal Caco-2 cells to a series of nine beta-receptor-blocking agents was investigated in vitro. The dynamic polar molecular surface area (PSAd) of the compounds was calculated from all low-energy conformations identified in molecular mechanics calculations in vacuum and in simulated chloroform and water environments. For most of the investigated drugs, the effects of the different environments on PSAd were small. The exception was H 216/44, which is a large flexible compound containing several functional groups capable of hydrogen bonding (PSAd,chloroform = 70.8 A2 and PSAd,water = 116.6 A2). The relationship between Pc and PSAd was stronger than those between Pc and the calculated octanol/water distribution coefficients (log Dcalc) or the experimentally determined immobilized liposome chromatography (ILC) retention. Pc values for two new practolol analogues and H 216/44 were predicted from the structure-permeability relationships of a subset of the nine compounds and compared with experimental values. The Pc values of the two practolol analogues were predicted well from both PSAd calculations and ILC retention studies. The Pc value of H 216/44 was reasonably well-predicted only from the PSAd of conformations preferred in vacuum and in water. The other descriptors overestimated the Pc of H 216/44 100-500-fold.

Inhibition of human alcohol dehydrogenases by formamides

Human alcohol dehydrogenase (HsADH) comprises class I (alpha, beta, and gamma), class II (pi), and class IV (sigma) enzymes. Selective inhibitors of the enzymes could be used to prevent the metabolism of alcohols that form toxic products. Formamides are unreactive analogues of aldehydes and bind to the enzyme-NADH complex [Ramaswamy, S.; Scholze, M.; Plapp, B. V. Biochemistry 1997, 36, 3522-3527]. They are uncompetitive inhibitors against varied concentrations of alcohol, and this makes them effective even with saturating concentrations of alcohols. Molecular modeling led to the design and synthesis of a series of cyclic, linear, and disubstituted formamides. Evaluation of 23 compounds provided structure-function information and selective inhibitors for the enzymes, which have overlapping but differing substrate specificities. Monosubstituted formamides are good inhibitors of class I and II enzymes, and disubstituted formamides are selective for the alpha enzyme. Selective inhibitors, with Ki values at pH 7 and 25 degrees C of 0.33-0.74 microM, include N-cyclopentyl-N-cyclobutylformamide for HsADH alpha, N-benzylformamide for HsADH beta1, N-1-methylheptylformamide for HsADH gamma2, and N-heptylformamide for HsADH sigma and HsADH beta1.