Specific markers of lipid peroxidation issued from n-3 and n-6 fatty acids.

Several markers of lipid peroxidation are available with different degrees of specificity, from malondialdehyde as a global marker, to F(2)-isoprostane, which is specifically produced from arachidonic acid. Among these, 4-hydroxynonenal is recognized as a breakdown product of fatty acid hydroperoxides, such as 15-hydroperoxy-eicosatetraenoic acid and 13-hydroperoxy-octade cadienoic acid from the n -6 fatty acids. Furthermore, 4-hydroxyhexenal (4-HHE) derives from n -3 fatty acid hydroperoxides. We have recently described the occurrence of 4-hydroxydodecadienal (4-HDDE) from the 12-lipoxygenase product of arachidonic acid 12-hydroperoxy-eicosatetraenoic acid. These three hydroxy-alkenals may be measured in human plasma by GC-MS, but they may partly be generated in the course of sampling, and the relative volatility of 4-HHE makes its measurement quite unreliable. We have successfully characterized and measured the stable oxidized carboxylic acid products from the hydroxy-alkenals 4-HNA, 4-HHA and 4-HDDA in urine. The ratio between 4-HHA and 4-HNA found in the same urinary sample might provide useful information on the location of lipid peroxidation, accounting for the high enrichment of the cerebrovascular system with docosahexaenoic acid, the main n -3 fatty acid in humans.

Synthesis of 9,9,9-trideutero-1,4-dihydroxynonane mercapturic acid (d3-DHN-MA), a useful internal standard for DHN-MA urinalysis.

Racemic 1,4-dihydroxynonane mercapturic acid (DHN-MA) and 9,9,9-trideutero-1,4-dihydroxynonane mercapturic acid (d3-DHN-MA) are synthesized on a 400-mg scale (overall yield approximately 40%) by a two-step sequence involving Michael addition of N-acetyl-L-cysteine to methyl 4-hydroxynon-2(E)-enoate or methyl 9,9,9-trideutero-4-hydroxynon-2 (E)-enoate, followed by reduction of the intermediate adducts with lithium borohydride. The requisite starting methyl esters are obtained, respectively, from heptanal or 7,7,7-trideuteroheptanal and methyl 4-chlorophenylsulfinylacetate via a sulfoxide piperidine and carbonyl reaction described in the literature. The 7,7,7-trideuteroheptanal is easily prepared by classical methods in four steps from 6-bromo-1-hexanol. 13C NMR data indicate that DHN-MA as well as d3-DHN-MA are obtained as mixtures of four diastereomers. Preliminary results show that d3-DHN-MA could be used as an internal standard for mass spectrometric quantification of DHN-MA in human urine.

Differential reactivity of alpha- and beta-anomers of glycosyl acceptors in glycosylations. A remote consequence of the endo-anomeric effect?

When phenyl tri-O-benzyl-1-thio-beta-D-galactopyranosiduronic acid esters were coupled with a 1/1 mixture of alpha and beta 2,3 di-O-protected D-galactopyranosiduronic acid esters, the beta-anomer proved to be more reactive. Data from theoretical calculations suggested that the enhanced reactivity of this anomer compared with the alpha one would be due to a stronger hydrogen bond of the C-4 OH with the ring oxygen.

Tandem mass spectrometric analysis of aspergillus niger pectin methylesterase: mode of action on fully methyl-esterified oligogalacturonates.

The substrate specificity and the mode of action of Aspergillus niger pectin methylesterase (PME) was determined using both fully methyl-esterified oligogalacturonates with degrees of polymerization (DP) 2-6 and chemically synthesized monomethyl trigalacturonates. The enzymic activity on the different substrates and a preliminary characterization of the reaction products were performed by using high-performance anion-exchange chromatography at neutral pH. Electrospray ionization tandem MS (ESI-MS/MS) was used to localize the methyl esters on the (18)O-labelled reaction products during the course of the enzymic reaction. A. niger PME is able to hydrolyse the methyl esters of fully methyl-esterified oligogalacturonates with DP 2, and preferentially hydrolyses the methyl esters located on the internal galacturonate residues, followed by hydrolysis of the methyl esters towards the reducing end. This PME is unable to hydrolyse the methyl ester of the galacturonate moiety at the non-reducing end.

Performance of selected microbial pectinases on synthetic monomethyl-esterified di- and trigalacturonates.

Two monomethyl esters of alpha-(1-4)-linked D-galacturonic dimers and three monomethyl esters of alpha-(1-4)-linked D-galacturonic acid trimers were synthesized chemically and further used as substrates in order to establish the substrate specificity of six different endopolygalacturonases from Aspergillus niger, one exopolygalacturonase from Aspergillus tubingensis, and four selected Erwinia chrysanthemi pectinases; exopolygalacturonan hydrolase X (PehX), exopolygalacturonate lyase X (PelX), exopectate lyase W (PelW), and oligogalacturonan lyase (Ogl). All A. niger endopolygalacturonases (PGs) were unable to hydrolyze the two monomethyldigalacturonates and 2-methyltrigalacturonate, whereas 1-methyltrigalacturonate was only cleaved by PGI, PGII, and PGB albeit at an extremely low rate. The hydrolysis of 3-methyltrigalacturonate into 2-methyldigalacturonate and galacturonate by all endopolygalacturonases demonstrates that these enzymes can accommodate a methylgalacturonate at subsite -2. The A. tubingensis exopolygalacturonase hydrolyzed the monomethyl-esterified digalacturonates and trigalacturonates although at lower rates than for the corresponding oligogalacturonates. 1-Methyltrigalacturonate was hydrolyzed at the same rate as trigalacturonate which demonstrates that the presence of a methyl ester at the third galacturonic acid from the nonreducing end does not have any effect on the performance of exopolygalacturonase. Of the four E. chrysanthemi pectinases, Ogl was the only enzyme able to cleave digalacturonate, whereas all four enzymes cleaved trigalacturonate. Ogl does not cleave monomethyl-esterified digalacturonate and trigalacturonate in case the second galacturonic acid residue from the reducing end is methyl-esterified. PehX did not hydrolyze any of the monomethyl-esterified trigalacturonates. The two lyases, PelX and PelW, were both only able to cleave 1-methyltrigalacturonate into Delta4,5-unsaturated 1-methyldigalacturonate and galacturonate.

Identification of the creatine binding domain of creatine kinase by photoaffinity labeling.

A new photoaffinity probe with a benzophenone group, N-dibenzylphospho-N'-(4-benzoyl)-benzylguanidine (BzPG), has been synthesized on the basis on our previously described creatine kinase bisubstrate analog. BzPG is also a bisubstrate type analog whose photoinsertion is inhibited by the natural substrates of creatine kinase. When rabbit CK-MM is irradiated in the presence of BzPG then cleaved by CNBr, one labeled peptide can be purified by reverse phase HPLC and sequenced. This sequence of 31 amino acids (Ala30-Val60) contains a region which could be responsible for isoenzyme selectivity and another one just preceding the 11 amino acid peptide (Asp61-Thr70) very recently described as a putative creatine binding site. This second peptide was deduced from the comparison of 18 amino acid sequence alignments. We proposed the creatine binding site to be essentially a peptide from Lys39 to Val71.

Synthesis of the two monomethyl esters of the disaccharide 4-O-alpha-D-galacturonosyl-D-galacturonic acid and of precursors for the preparation of higher oligomers methyl uronated in definite sequences.

Methyl (alpha-D-galactopyranosyluronic acid)-(1-->4)-D-galactopyranuronate and methyl alpha-D-galactopyranosyl-uronate-(1-->4)-D-galactopyranuronic acid have been synthesized by coupling methyl (benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate (3) or benzyl (benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate (4) with benzyl (phenyl 2,3,4-tri-O-benzyl-1-thio-beta-D-galactopyranosid)uronate and methyl (phenyl 2,3,4-tri-O-benzyl-1-thio-beta-D-galactopyranosid)uronate, respectively, using N-iodosuccinimide and trifluoromethanesulphonic acid as promoters, followed by removal of the benzyl groups. The 4'-OH unprotected dimers benzyl (methyl 2,3-di-O-benzyl-alpha-D-galactopyranosyluronate)-(1-->4)-(benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate and methyl (benzyl 2,3-di-O-benzyl-alpha-D-galactopyranosyluronate)-(1-->4)-(benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate were prepared from methyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-beta-D-galactopyranosid) uronate and benzyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-beta-D-galactopyranosid) uronate and acceptors 4 or 3, respectively. These compounds have been designed to serve as precursors for the preparation of higher-membered D-galacturonic acid oligomers methyl esterified in definite positions.

N-dibenzylphospho-N'-3-(2,6-dichlorophenyl)propyl-guanidine is a bisubstrate-analog for creatine kinase.

We describe a new compound, N-dibenzylphospho-N'-3-(2,6-dichlorophenyl)-propylguanidine (DPPG), and our study of its interaction with cytosolic CK. To our knowledge, it is the most potent inhibitor known for CK: the Ki value versus ADP was 330 nM and 110 nM for CK-MM and BB respectively. In view of the inhibition pattern, Ki(app) dependencies on the second substrate, and very low Ki values, we conclude that DPPG binds to the active site as a bisubstrate-type analog. This bisubstrate analog confirms different mechanisms for CK-MM and BB: in spite of a more than 80% similarity in amino-acid sequences, both isoenzymes are random at pH 8.6 but CK-BB has an ordered mechanism at pH 6.6.

Dichloroaromatic phosphoguanidines are potent inhibitors but very poor substrates for cytosolic creatine kinase.

New phosphorylated guanidines have been synthesized and examined as potential inhibitors for creatine kinase. These compounds show a significant increase of inhibitory activity in comparison with the corresponding guanidines. Unlike the guanidines, they are competitive inhibitors because of the phosphoryl group. N-Phospho-N'-2-(2,6-dichlorophenyl)ethylguanidine is a potent inhibitor (K(i) = 2.0 mM and 1.2 mM respectively for muscle and brain-type creatine kinase). Although these phosphorylated analogs of creatine phosphate have a very poor substrate activity in the reverse reaction, the phosphoryl group is important for binding to the enzyme.

A novel synthetic reversible inhibitor of sialidase efficiently blocks secondary but not primary influenza virus infection of MDCK cells in culture.

The sodium salts of 2-difluoromethyl-phenyl-alpha-ketoside of N-acetyl-neuraminic acid (compound 1) and of 4-difluoromethyl-2-methoxy-phenyl-alpha-ketoside of N-acetylneuraminic acid (compound 2) were designed as potential mechanism-based inhibitors of sialidase. In vitro both of these compounds competitively inhibited the sialidases of Clostridium perfringens and of influenza virus A/HK/1/68. Inhibition was irreversible with the sialidase of Clostridium perfringens whereas it was reversible with that of A/HK/1/68. Compound 2 did not inhibit the hemagglutinin of the virus but exhibited significant anti-influenza activity when added to the medium of Madin-Darby canine kidney (MDCK) cells infected by influenza virus. In non-infected MDCK cells no inhibition of cellular sialidase was observed. Compound 2 did not block primary infection, but inhibited the release of progeny virus from infected cells. Even after 8 passages in its presence, no resistant strains were detected. Because of its high Ki (8 x 10(-5) M) compared to the low Ki (1' x 1(-10) M) of 4 guanidino-Neu 5 Ac 2en and its reversible inhibition of viral sialidase, its development as an anti-influenza agent is no longer envisaged. Nevertheless, as a mechanism-based irreversible inhibitor of the bacterial enzyme, it could at least be useful for investigating the intrinsic role of sialidase in infections caused by this strain.

A novel synthetic reversible inhibitor of sialidase efficiently blocks secondary but not primary influenza virus infection of MDCK cells in culture.

The sodium salts of 2-difluoromethyl-phenyl-α-ketoside of N-acetyl-neuraminic acid (compound 1) and of 4-difluoromethyl-2-methoxy-phenyl-α-ketoside of N-acetylneuraminic acid (compound 2) were designed as potential mechanism-based inhibitors of sialidase. In vitro both of these compounds competitively inhibited the sialidases of Clostridium perfringens and of influenza virus A/HK/1/68. Inhibition was irreversible with the sialidase of Clostridium perfringens whereas it was reversible with that of A/HK/1/68. Compound 2 did not inhibit the hemagglutinin of the virus but exhibited significant anti-influenza activity when added to the medium of Madin-Darby canine kidney (MDCK) cells infected by influenza virus. In non-infected MDCK cells no inhibition of cellular sialidase was observed. Compound 2 did not block primary infection, but inhibited the release of progeny virus from infected cells. Even after 8 passages in its presence, no resistant strains were detected. Because of its high Ki (8 × 10-5M) compared to the low Ki (1 × 1-10 M) of 4 guanidino-Neu 5 Ac 2en and its reversible inhibition of viral sialidase, its development as an anti-influenza agent is no longer envisaged. Nevertheless, as a mechanism-based irreversible inhibitor of the bacterial enzyme, it could at least be useful for investigating the intrinsic role of sialidase in infections caused by this strain.

Synthesis and differential properties of creatine analogues as inhibitors for human creatine kinase isoenzymes.

Fourteen new creatine analogues, all with a guanidine function and either a polar or an apolar group instead of the creatine carboxylic function, were tested as potential inhibitors for human creatine kinase by kinetic analysis of their effects on the reaction rate. Only compounds bearing an apolar aromatic moiety, which was spaced from the guanidine function by at least two bonds, proved to have a significant inhibitory activity and showed a mixed-type inhibition similar to that of creatine. Among these compounds 2,6-dichlorobenzylguanidine (Ki = 5.6 mM and 39.8 mM for muscle-type and brain-type creatine kinases, respectively) and 3-(2,6-dichlorophenyl)propylguanidine (Ki = 15 mM and 4.5 mM) were the more potent inhibitors and showed a significant isoenzyme selectivity between muscle- and brain-type creatine kinases. Our results are in agreement with recent data that suggest the location of a hydrophobic pocket near the guanidine-binding domain of the enzyme. The observed selectivity in isoenzyme inhibition may be useful to study structural differences in catalytic centers.

Altered methional homoeostasis is associated with decreased apoptosis in BAF3 bcl2 murine lymphoid cells.

Methional is a potent inducer of apoptosis in an interleukin 3-dependent murine lymphoid cell line BAF3 b0 when it is added to the culture medium. In these cells transfected with the bcl2 gene, BAF3 bcl2, the apoptotic-inducing activity of methional is dramatically reduced. The addition of disulfiram (an inhibitor of aldehyde dehydrogenase) in order to reduce methional oxidation brought about an increase in apoptosis in BAF3 b0 but not in BAF3 bcl2 cells. In contrast, the addition of quercetin (an inhibitor of aldehyde reductase) in an attempt to diminish methional reduction increased apoptosis in both BAF3 b0 and BAF3 bcl2 cells. The extent of DNA fragmentation in BAF3 bcl2 cells approached that in BAF3 b0 cells in the presence of quercetin and exogenous methional, suggesting a defect in methional biosynthesis in BAF3 bcl2 cells. Direct evidence for this was obtained by measuring labelled methional in cells incubated with the sodium, salt of [U-14C]4-methylthio-2-oxobutanoic acid (MTOB), the precursor of methional. The 80% decrease in labelled methional in BAF3 bcl2 compared with BAF3 b0 cells was accompanied by a concomitant rise in the transamination of [14C]MTOB to [14C]methionine in BAF3 bcl2 cells. Inhibition of the transaminase, however, by a synthetic transition-state-type compound, pyridoxal-L-methionine ethyl ester, induced apoptosis in BAF3 b0 but not in BAF3 bcl2 cells, confirming that the defect in BAF3 bcl2 cells was not in the transaminase itself but rather in the oxidative decarboxylation step MTOB --> methional. In addition, no evidence was obtained for the synthesis of [14C]malondialdehyde from [14C]methional in BAF3 bcl2 cells. As these cells show no deficiency in their content of reactive oxygen species compared with that of BAF3 b0 cells, they may possess some other defect in the beta-hydroxylase enzyme system itself.

Synthesis of transition-state analogues as potential inhibitors of sialidase from Influenza virus.

Sodium 5-acetamido-2,6-anhydro-3,4,5-trideoxy-D-manno-non-2-enonate (2) has been synthesized from N-acetyl-4-deoxy-neuraminic acid methyl ester (4). Sodium 2,6-anhydro-3-deoxy-L-arabino-hept-2-enonate (3), 4-acetamido-2,6-anhydro-3,4-dideoxy-L-arabino-hept-2-enonic acid (18e), and 4-acetamido-2,6-anhydro-3,4-dideoxy-L-ribo-hept-2-enonic acid (18a) have been prepared from L-arabinose. The above compounds were investigated as inhibitors of sialidase from Influenza virus. Only compound 2 showed a significant inhibitory activity (Ki 8 x 10(-2) mM) against the enzyme.

Contribution of 4-methylthio-2-oxobutanoate and its transaminase to the growth of methionine-dependent cells in culture. Effect of transaminase inhibitors.

The growth in culture of methionine-dependent transformed cells of human, rat and mouse origin was arrested in the absence of L-methionine (Met) but took place in the presence of 4-methylthio-2-oxobutanoic acid (MTOB), the keto acid of Met. From 24 hr after seeding, cells grew in 0.1 mM MTOB medium at a rate comparable to that in 0.1 mM Met medium. Using [35S]MTOB, it was found that the Met synthesized was used in normal MRC-5 cells and in transformed HeLa cells to the same extent for protein, adenosylmethionine and adenosylhomocysteine syntheses. However, when the free Met content was examined, it was found to be 3-fold greater in HeLa than in MRC-5 cells. To examine the importance of this free Met for the growth of transformed cells, the transaminase responsible for converting MTOB to Met was chosen as a target enzyme for the synthesis of compounds with potential inhibitory activity. Since this is a multisubstrate enzyme, reduced Schiff bases were prepared containing both pyridoxal or other aromatic groups, as one constituent, and L-Met or other amino-acids in the free acid or ester or amide form, as the other constituent. Only esters containing the pyridoxal moiety and Met or certain of its structural analogues exhibited good selective growth inhibitory activity in that there was little (20%) or no effect on the growth of normal MRC-5 and derm cells, respectively, while that of transformed HeLa, HEp-2 and L1210 cells was strongly inhibited (80%). This inhibition was accompanied by a concomitant decrease in the activity of the MTOB transaminase in both HeLa and MRC-5 cells treated with 3c the most potent inhibitor. However, using [35S]MTOB it was found that MTOB itself accumulated 48% in HeLa but only 12% in MRC-5 cells treated with 3c. On the contrary [35S]Met formed from [35S]MTOB increased 3.7-fold in MRC-5 inhibitor-treated cells showing 20% growth inhibition whereas it decreased 38% in HeLa-treated cells showing 80% growth inhibition. This decrease in cellular Met in HeLa is not responsible for growth arrest. Indeed the growth of HeLa cells could not be restored by adding a 10-fold excess of Met. Since MTOB can alleviate Met-dependence, the intracellular homeostasis of this metabolite may play a hitherto unsuspected role in controlling cell growth.

In vivo antitumor activity of 4-amino 4-methyl 2-pentyne 1-al, an inhibitor of aldehyde dehydrogenase.

4-amino-4-methyl-2-pentyne-1-al (AMPAL), a new irreversible inhibitor of aldehyde dehydrogenase (ALDH) has been assayed for its in vitro and in vivo antitumor activity. In vitro, AMPAL inhibits the proliferation and the ALDH activity of L1210 and RBL5 cell lines. In vivo, AMPAL significantly increases the mean survival time of mice i.p. grafted with leukemia (L1210, P815, MBL2, EL4, RBL5 cell lines) or carcinoma cells (Krebs cell line), without haematopoetic toxicity. No carcinostatic effect was observed against the P388 leukemia and the 3LL Lewis lung carcinoma. A possible relationship between the ALDH isoenzyme activity of the tumor and its sensitivity to AMPAL is discussed in the light of previous reports concerning the role of aldehydes in cell growth control.

The effect of a novel inhibitor of aldehyde dehydrogenase on viral replication.

The effect of AMPAL (4-amino 4-methyl 2-pentyne 1-al), an inhibitor of aldehyde dehydrogenase, on adenovirus type 5 (Ad5) replication was studied. AMPAL at 2 x 10(-4) M clearly reduced the cytopathic effect on HeLa cells but had no effect on cell growth at this concentration. Viral adsorption, penetration and protein synthesis were not affected by adding AMPAL at 2 hr post infection. When viral DNA synthesized in the presence of AMPAL was investigated, no significant inhibition was observed on either synthesis or the physicochemical properties of the neosynthesized DNA. However, there was a 4-fold increase in the amount of condensed DNA. In addition, AMPAL inhibited intracellular viral production (40%) and brought about concomitant inhibition of virus release (70%) into the medium. The absence of a quantitative relationship between the inhibition of viral DNA synthesis on one hand and that of viral production on the other may imply that the antiviral effect of AMPAL is indirectly mediated by the action of the malondialdehyde which has accumulated on some, as not yet identified, membrane constituent.

Malondialdehyde production from spermine by homogenates of normal and transformed cells.

The oxidation of spermine in vitro by a mixture of polyamine oxidase and diamine oxidase from pig kidney gives rise to malondialdehyde via 3-aminopropanol as the intermediate. Conversely, with spermidine, under similar experimental conditions, no evidence could be obtained for malondialdehyde formation within the limits of sensitivity of the assay (2.0 nmol). The activities of both these enzymes show about a 2-fold increase in normal rat kidney cells (LA31 NRK) transformed by the temperature sensitive mutant of Rous sarcoma virus (LA31) and incubated at the non permissive temperature (39 degrees C) compared to the activities in LA31 NRK at the permissive temperature (33 degrees C). These same enzymatic activities show no temperature dependent changes in normal rat kidney cells (NRK) or in these same cells infected by the wild type virus (NRK B77). In extracts derived from Friend erythroleukemic cells induced to differentiate by dimethyl sulfoxide or hexamethylene bis acetamide, spermine oxidation takes place more efficiently than in non induced cells. A rise in diamine oxidase activity is seen in LA31 NRK (39 degrees C) 12 h after the temperature shift, whereas morphological manifestations of normalcy are seen only at 48 h. The Km of diamine oxidase is 10(-6) M for putrescine and 10(-3) M for 3-aminopropanol. A possible mechanism involving the well documented acetylation of putrescine [23,26] is proposed for diverting intracellular putrescine away from cytosolic diamine oxidase and towards intramitochondrial monoamine oxidase.