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PubMed2003

Addendum to Food Additives and Contaminants 2002, 19, 492-501 migration of monomers from liquid crystalline poly(p-hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid).

Liquid-crystalline co-polyesters (e.g. a random copolyester based on p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) known as Vectra A950) offer good barrier properties, but for food-contact use they require overall and specific migration testing. For Vectra A950 films, the highest overall migration level obtained was 2.3 mg x dm(-2) (13.8 mg x kg(-1)) in olive oil (10 days at 40 degrees C), well below the EC limit of 10 mg dm(-2) (60 mg x kg(-1)). The highest specific migration of HBA was 15.2 microg x dm(-2) (91.2 microg x kg(-1)) in olive oil (2 h at 175 degrees C). In this case, the migration level was well below the EC limit of 10 mg dm(-2) (60 mg x kg(-1)). For HNA, the highest value obtained was 4.3 microg x dm(-2) (26 microg x kg(-1)) in 10% ethanol (4 h at 100 degrees C), well below the specific migration limit (SML = 50 microg x kg(-1)). The results obtained shows that even at these severe conditions, the migration values comply with the new European Union Directive 2002/72/EC, which regulates plastic materials and articles for food contact use. In addition, the polymer Vectra A950 complies with Food Contact Notification (FCN) No. 103 of the United States Food and Drug Administration (FDA). Vectra A950 is therefore permitted for food-contact use both in the European Union and the USA.

Chromatography, High Pressure Liquid↗
PubMed1992

The conformational behaviour of complexes of alpha-cyclodextrin with p-chlorophenol and p-hydroxybenzoic acid in water as studied by molecular dynamics simulations.

Molecular dynamics simulations were performed to obtain information about the conformational behaviour and stabilization of alpha-cyclodextrin (alpha CD) complexes in water. Simulations of p-chlorophenol and p-hydroxybenzoic acid in alpha CD showed that the complex is a very flexible system. The guest compound rotates inside the cavity and partly moves in and out. alpha CD continuously adapts its conformation to the orientation of the guest compound (or vice versa): the hexagon of the glycosidic oxygen atoms is stretched parallel to the plane of the aromatic ring of the guest compound during 80% of the simulation. This suggests that Van der Waals interactions play an important role in the stabilization of the complex. Each intramolecular hydrogen bond between neighbouring glucose units is formed during 30-80% of the simulation. Hydrogen bonds between alpha CD and the guest compound, on the other hand, are rarely formed. Thus, intermolecular hydrogen bonding seems to play a minor role in the stabilization of alpha CD complexes.

Chlorophenols↗
PubMed2006

Reaction of para-hydroxybenzoic acid esters with singlet oxygen in the presence of glutathione produces glutathione conjugates of hydroquinone, potent inducers of oxidative stress.

The determination and toxicological characterization of products of the reaction between p-hydroxybenzoic acid esters (parabens) and singlet oxygen ((1)O(2)) are very important because of the frequent use of parabens in cosmetics and possible generation of (1)O(2) in the skin. We observed (1)O(2)-dependent production of mono-, di-, and tri-substituted glutathione (GSH) conjugates of hydroquinone (HQ) during visible light-irradiation of a mixture of methyl or ethyl paraben and GSH in the presence of rose bengal (RB). 1,4-Benzoquinone (BQ) and HQ were produced during the irradiation in the absence of GSH. While a mixture of BQ and GSH produced only mono-substituted conjugate, irradiation of the mixture with RB produced mono-, di-, and tri-substituted conjugates. These observations indicate that (1)O(2) is involved both in the production of BQ and HQ from parabens and in the formation of multi-substituted GSH conjugates from mono-substituted conjugate. Tri-substituted conjugate generated larger amounts of hydrogen peroxide in an aqueous solution than mono-substituted conjugates or HQ did. Detection of semiquinone radical suggests that the autoxidation of conjugates is related to the generation of hydrogen peroxide. The results obtained in this study indicate that parabens may induce oxidative stress in the skin after conversion to GSH conjugates of HQ by reacting with (1)O(2) and GSH.

Chromatography, High Pressure Liquid↗
PubMed2000

Adsorption of esters of p-hydroxybenzoic acid by filter membranes: mechanism and effect of formulation and processing parameters.

The adsorption of esters of p-hydroxybenzoic acid (parabens) by filter membranes was studied by a flow-through technique. The hydrophobic effect was the major mechanism of adsorption. Propylparaben was more extensively adsorbed by all the membranes than was methylparaben. Hydrophobic membranes exhibited the greatest degree of adsorption, whereas adsorption was minimal for hydrophilic membranes. The charge of the filter membrane did not affect paraben adsorption. Formulation factors studied included the concentration of paraben, the presence of a tonicity-modifying agent (sodium chloride, mannitol, glycerin), and the presence of a chelating agent (edetate sodium). Paraben adsorption was directly related to paraben concentration. The presence of a tonicity modifier or chelating agent did not alter paraben adsorption to membrane filters. Processing parameters studied included flow rate, temperature, autoclaving, flow interruption, and filter membrane presaturation. Presaturation of the filter membranes for up to 1 hr reduced but did not eliminate paraben adsorption during simulated use. Interrupting the flow of the paraben solution through the filter membrane allowed for additional paraben adsorption and caused the concentration of paraben in the restarted filtrate to be less than 100% of theory.

Adsorption↗
PubMed2005

A mutation in para-hydroxybenzoate-polyprenyl transferase (COQ2) causes primary coenzyme Q10 deficiency.

Ubiquinone (coenzyme Q(10) or CoQ(10)) is a lipid-soluble component of virtually all cell membranes, where it functions as a mobile electron and proton carrier. CoQ(10) deficiency is inherited as an autosomal recessive trait and has been associated with three main clinical phenotypes: a predominantly myopathic form with central nervous system involvement, an infantile encephalomyopathy with renal dysfunction, and an ataxic form with cerebellar atrophy. In two siblings of consanguineous parents with the infantile form of CoQ(10) deficiency, we identified a homozygous missense mutation in the COQ2 gene, which encodes para-hydroxybenzoate-polyprenyl transferase. The A-->G transition at nucleotide 890 changes a highly conserved tyrosine to cysteine at amino acid 297 within a predicted transmembrane domain. Radioisotope assays confirmed a severe defect of CoQ(10) biosynthesis in the fibroblasts of one patient. This mutation in COQ2 is the first molecular cause of primary CoQ(10) deficiency.

Alkyl and Aryl Transferases↗
PubMed1991

Metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol in human mammary epithelial cells: feedback inhibition by 7-hydroxybenzo[a]pyrene.

The metabolism of benzo[a]pyrene (B[a]P) and (-)-transbenzo[a]pyrene-7,8-dihydrodiol (B[a]P-diol) was compared in human mammary epithelial cells (HMEC) grown in serum-free medium, MCDB-170. Conversion of B[a]P-diol to the carcinogen (+)-benzo[a]pyrene-7,8-dihydroxy-9,10-epoxide (BPDE), as measured by analysis of their tetraol hydrolysis products, occurred much more efficiently in cultures incubated with [3H]B[a]P-diol than in cultures incubated with [3H]B[a]P. In cultures pretreated with unlabeled B[a]P (24 h, 400 nM), the conversion of [3H]-B[a]P-diol to [3H]tetraols is inhibited 49%, while the conversion of [3H]B[a]P to [3H]B[a]P-diol- is not affected. These observations led to the identification of a major B[a]P-derived metabolite as 7-hydroxybenzo[a]pyrene (B[a]P-7-ol), which was found to be an extremely potent and selective inhibitor of the conversion of B[a]P-diol to BPDE, with a KI estimated at 3-12 nM. Thus B[a]P activation in HMEC appears to be significantly limited by a feedback inhibition pathway induced by B[a]P-7-ol. The potency and selectivity of the B[a]P-7-ol-induced inhibition suggests that the diol to diolepoxide conversion is affected by a selective oxygenase in HMEC, rather than a non-enzymatic, peroxy radical-induced mechanism. B[a]P-7-ol should prove to be a valuable tool in the study of B[a]P carcinogenesis.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1984

The identification of bases in DNA involved in covalent binding of the reactive metabolite from 9-hydroxybenzo[a]pyrene.

Unlabelled 9-hydroxybenzo[a]pyrene (9-OH-BP) was incubated with a microsomal metabolic system and plasmid Col E1 DNA that had been radiolabelled by nick-translation with a tritiated deoxyribonucleotide. After the addition of an excess of a similar incubate that substituted calf thymus for plasmid DNA, a fraction obtained from DNA hydrolysates of these incubation mixtures was analysed by reverse-phase, h.p.l.c. for fluorescence and radioactivity of eluates. The presence of radioactivity with fluorescence activity in the same eluate fractions indicated the presence of 9-OH-BP-derived adducts with that radiolabelled nucleoside. These analyses showed the presence of at least four adducts with dG, a single adduct with dA, and no adducts with either dC or dT in plasmid DNA. This enabled the identification of components of similar h.p.l.c. profiles obtained from incubates with calf thymus DNA and [3H]9-OH-BP. No major qualitative or quantitative differences were found. As both the identities and extent of binding to these bases were similar to these previously reported for the ultimately carcinogenic BP- diolepoxides , we conclude that the non-carcinogenicity of 9-OH-BP is not, therefore, attributed to a difference in the base moieties involved in adduct formation. H.p.l.c. and spectrofluorimetric analyses indicated that an isolated metabolite of 9-OH-BP is indistinguishable from its 4,5-dihydrodiol. This is interpreted as evidence for the formation of 9-OH-BP-4,5-oxide as the reactive, DNA-binding intermediate.

Animals↗
PubMed1984

The lack of transformation activity of 9-hydroxybenzo[a]pyrene related to the absence of modified deoxyribonucleosides in DNA of C3H/10T1/2 cells.

Sephadex LH-20 chromatography of DNA digests of C3H/10T1/2 cells treated with [3H]9-hydroxybenzo[a]pyrene (9-OH-BaP) and [14C]BaP-7,8-diol showed: (i) the presence only of uncharacterized 3H radioactivity eluted in the early portion of the gradient; [3H]9-OH-BaP-4,5-oxide-modified deoxyribonucleosides were not observed. (ii) The total amount of [14C]-labelled radioactivity corresponded to nucleoside moieties which were modified by anti- and syn-benzo[a]pyrene diol-epoxide. The absence of nucleosides modified by 9-OH-BaP-4,5-oxide in C3H/10T1/2 cells observed in this study may account in part for the relative resistance of these cells to the mutagenic and transforming action of 9-OH-BaP.

Animals↗
PubMed2000

Oral bioavailability and pharmacokinetics of elimination of 9-hydroxybenzo[a]pyrene and its glucoside and sulfate conjugates after administration to male and female American lobsters, Homarus americanus.

The pharmacokinetics of [(3)H]-9-hydroxybenzo[a]pyrene (9-OH-BaP), a highly lipophilic primary metabolite of benzo(a)pyrene, were examined after intrapericardial (iv) or oral doses of 50 or 200 microg/kg to intermolt American lobsters, Homarus americanus. Combining data for all lobsters, the average terminal elimination half-life of parent 9-OH-BaP was 97.3 h after iv and 56.5 h after oral administration, considerably less than found previously for benzo(a)pyrene (720 h). The oral bioavailability of parent 9-OH-BaP, calculated from the area under the hemolymph concentration curve, was 15.9%. The low bioavailability and variable elimination rates were attributed to extensive first-pass conjugation and sequestration in the hepatopancreas. BaP-9-sulfate was the major metabolite. Hemolymph concentrations of BaP-9-sulfate increased up to one day after the dose, and then decreased, with a terminal elimination half-life of 45 h. BaP 9-beta-D-glucoside was a minor metabolite in most hemolymph and tissue samples; an exception was hemolymph from the iv high-dose group. Concentrations of 9-OH-BaP and metabolites in the edible muscle tissue were similar to those in hemolymph, and 9-OH-BaP residues at 10 to 16 days after the dose were 3 to 12 ng/g muscle. Sulfotransferase and UDP-glucosyltransferase (UGT) activities with 9-OH-BaP were found in the antennal gland, intestinal mucosa, and hepatopancreas (UGT only). Sulfatase activity with BaP-9-sulfate, found in both the hepatopancreas and the antennal gland, was thought to contribute to metabolite cycling. These studies showed that 9-OH-BaP was readily conjugated to sulfate and glucose in the lobster, and that despite their high lipophilicity, 9-OH-BaP and conjugates were excreted from the lobster hemolymph and tissues much more rapidly than benzo[a]pyrene.

Administration, Oral↗
PubMed1993

Mutants of Escherichia coli affected in respiration: the cloning and nucleotide sequence of ubiA, encoding the membrane-bound p-hydroxybenzoate:octaprenyltransferase.

A mutant of Escherichia coli has been isolated that is unable to grow aerobically on non-fermentable substrates, but able to grow anaerobically on glycerol with alternative electron acceptors such as fumarate. Nitrate as electron acceptor supports anaerobic growth on glycerol, but not on succinate or lactate. Oxygen consumption rates by cell-free extracts with succinate, lactate or glycerol 3-phosphate as substrates were low relative to activities in an isogenic control strain but were restored in vitro by adding ubiquinone-1. Transformation of the mutant with a cloned 2.6 kb ClaI-PvuII fragment of chromosomal DNA restored cellular quinone levels and growth on succinate. The plasmid also complemented a previously isolated ubiA mutant for aerobic growth on non-fermentable substrates. The nucleotide sequence of the cloned fragment revealed a fragment of plsB (91.7 min on the E. coli chromosome map) and three open reading frames (ORFs), one of which (ORF3) encodes a protein with a predicted molecular mass of 32511 Da. The hydrophobicity profile of the ORF3 protein is characteristic of a membrane protein with five hydrophobic regions and is very similar to that of the Saccharomyces cerevisiae COQ2 gene product (p-hydroxybenzoate:polyprenyltransferase, required for the second step of ubiquinone biosynthesis) and to the product of the E. coli cyoE gene. Complementation of ubi mutants with various deletion derivatives of the cloned DNA fragment confirms that ORF3 is ubiA. ORF3 is closely linked to ubiC (ORF2), which encodes chorismate lyase.

Alkyl and Aryl Transferases↗
PubMed2005

Cryptanaerobacter phenolicus gen. nov., sp. nov., an anaerobe that transforms phenol into benzoate via 4-hydroxybenzoate.

An anaerobic bacterium that transforms phenol and 4-hydroxybenzoate (4-OHB) into benzoate, strain LR7.2T, was isolated from a culture originating from a mixture of swamp water, sewage sludge, swine waste and soil. Cells of strain LR7.2T are Gram-positive short rods (1 x 2 microm) that are electron-dense when observed by electron microscopy. The optimum pH and temperature for growth and transformation activity of 4-OHB are 7.5-8.0 and 30-37 degrees C, respectively. The bacterium does not use sulphate, thiosulphate, nitrate, nitrite, FeCl3, fumarate or arsenate as an electron acceptor. It does not normally use sulphite, although stimulation of growth and 4-OHB transformation activity at a low concentration (up to 2 mM) has been reported previously under different culture conditions. The presence of 4-OHB or phenol is essential for growth; transformation of 4-OHB or phenol into benzoate is used to produce energy for growth. Using [6D]-phenol, 4-OHB was shown to be an intermediate in the transformation of phenol into benzoate. No spore was observed. The bacterium has a DNA G+C content of 51 mol% and its major membrane fatty acid is anteiso-C(15 : 0). The 16S rRNA gene sequence of strain LR7.2T shows only 90 % similarity to its closest relative (Pelotomaculum thermopropionicum). From these results, a new taxon is proposed: Cryptanaerobacter phenolicus gen. nov., sp. nov. The type strain is LR7.2T (=ATCC BAA-820T=DSM 15808T).

Anaerobiosis↗
PubMed1993

Elicitor-Induced Changes in Ca2+ Influx, K+ Efflux, and 4-Hydroxybenzoic Acid Synthesis in Protoplasts of Daucus carota L.

Suspension-cultured carrot cells (Daucus carota) and their protoplasts respond to a fungal elicitor prepared from the culture medium of Pythium aphanidermatum by accumulating 4-hydroxybenzoic acid (4-HBA). Protoplasts release the compound into the culture medium. Using 45CaCl2 as a tracer, we were able to demonstrate that the secretion of 4-HBA is preceded by a rapid increase in the Ca2+ influx and a concomitant K+ efflux. If the increased Ca2+ influx was prevented by ethyleneglycol-bis([beta]-aminoethylether)-N,N[prime]-tetraacetic acid, 4-HBA synthesis was inhibited by 70%. These results are discussed with regard to signal transduction from the plasma membrane to the nucleus of carrot protoplasts.

Journal Article↗
PubMed2004

Metabolic engineering of the chloroplast genome using the Echerichia coli ubiC gene reveals that chorismate is a readily abundant plant precursor for p-hydroxybenzoic acid biosynthesis.

p-Hydroxybenzoic acid (pHBA) is the major monomer in liquid crystal polymers. In this study, the Escherichia coli ubiC gene that codes for chorismate pyruvate-lyase (CPL) was integrated into the tobacco (Nicotiana tabacum) chloroplast genome under the control of the light-regulated psbA 5' untranslated region. CPL catalyzes the direct conversion of chorismate, an important branch point intermediate in the shikimate pathway that is exclusively synthesized in plastids, to pHBA and pyruvate. The leaf content of pHBA glucose conjugates in fully mature T1 plants exposed to continuous light (total pooled material) varied between 13% and 18% dry weight, while the oldest leaves had levels as high as 26.5% dry weight. The latter value is 50-fold higher than the best value reported for nuclear-transformed tobacco plants expressing a chloroplast-targeted version of CPL. Despite the massive diversion of chorismate to pHBA, the plastid-transformed plants and control plants were indistinguishable. The highest CPL enzyme activity in pooled leaf material from adult T1 plants was 50,783 pkat/mg of protein, which is equivalent to approximately 35% of the total soluble protein and approximately 250 times higher than the highest reported value for nuclear transformation. These experiments demonstrate that the current limitation for pHBA production in nuclear-transformed plants is CPL enzyme activity, and that the process becomes substrate-limited only when the enzyme is present at very high levels in the compartment of interest, such as the case with plastid transformation. Integration of CPL into the chloroplast genome provides a dramatic demonstration of the high-flux potential of the shikimate pathway for chorismate biosynthesis, and could prove to be a cost-effective route to pHBA. Moreover, exploiting this strategy to create an artificial metabolic sink for chorismate could provide new insight on regulation of the plant shikimate pathway and its complex interactions with downstream branches of secondary metabolism, which is currently poorly understood.

Chloroplasts↗
PubMed1996

Genetic engineering of plant secondary metabolism. Accumulation of 4-hydroxybenzoate glucosides as a result of the expression of the bacterial ubiC gene in tobacco.

The ubiC gene of Escherichia coli encodes chorismate pyruvatelyase, an enzyme that converts chorismate into 4-hydroxybenzoate (4HB) and is not normally present in plants. The ubiC gene was expressed in Nicotiana tabacum L. plants under control of a constitutive plant promoter. The gene product was targeted into the plastid by fusing it to the sequence for the chloroplast transit peptide of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Transgenic plants showed high chorismate pyruvate-lyase activity and accumulated 4HB as beta-glucosides, with the glucose attached to either the hydroxy or the carboxyl function of 4HB. The total content of 4HB glucosides was approximately 0.52% of dry weight, which exceeded the content of untransformed plants by at least a factor of 1000. Feeding experiments with [1,7-13C2]shikimic acid unequivocally proved that the 4HB that was formed in the transgenic plants was not derived from the conventional phenylpropanoid pathway but from the newly introduced chorismate pyruvate-lyase reaction.

Amino Acid Sequence↗
PubMed1998

Accumulation of salicylic acid and 4-hydroxybenzoic acid in phloem fluids of cucumber during systemic acquired resistance is preceded by a transient increase in phenylalanine ammonia-lyase activity in petioles and stems.

Cucumber (Cucumis sativa) leaves infiltrated with Pseudomonas syringae pv. syringae cells produced a mobile signal for systemic acquired resistance between 3 and 6 h after inoculation. The production of a mobile signal by inoculated leaves was followed by a transient increase in phenylalanine ammonia-lyase (PAL) activity in the petioles of inoculated leaves and in stems above inoculated leaves; with peaks in activity at 9 and 12 h, respectively, after inoculation. In contrast, PAL activity in inoculated leaves continued to rise slowly for at least 18 h. No increases in PAL activity were detected in healthy leaves of inoculated plants. Two benzoic acid derivatives, salicylic acid (SA) and 4-hydroxybenzoic acid (4HBA), began to accumulate in phloem fluids at about the time PAL activity began to increase, reaching maximum concentrations 15 h after inoculation. The accumulation of SA and 4HBA in phloem fluids was unaffected by the removal of all leaves 6 h after inoculation, and seedlings excised from roots prior to inoculation still accumulated high levels of SA and 4HBA. These results suggest that SA and 4HBA are synthesized de novo in stems and petioles in response to a mobile signal from the inoculated leaf.

Cucumis sativus↗
PubMed1990

Phenylpropanoid Metabolism in Suspension Cultures of Vanilla planifolia Andr. : III. Conversion of 4-Methoxycinnamic Acids into 4-Hydroxybenzoic Acids.

Feeding of 4-methoxycinnamic acid, 3,4-dimethoxycinnamic acid and 3,4,5-trimethoxycinnamic acid to cell suspension cultures of Vanilla planifolia resulted in the formation of 4-hydroxybenzoic acid, vanillic acid, and syringic acid, respectively. The homologous 4-methoxybenzoic acids were demethylated to the same products. It is concluded that the side chain degrading enzyme system accepts the 4-methoxylated substrates while the demethylation occurs at the benzoic acid level. The demethylating enzyme is specific for the 4-position. Feeding of [O-(14)C-methyl]-3,4-dimethoxycinnamic acid revealed that the first step in the conversion is the glycosylation of the cinnamic acid to its glucose ester. A partial purification of a UDP-glucose: trans-cinnamic acid glucosyltransferase is reported. 4-Methoxy substituted cinnamic acids are better substrates for this enzyme than 4-hydroxy substituted cinnamic acid. It is suggested that 4-methoxy substituted cinnamic acids are intermediates in the biosynthetic conversion of cinnamic acids to benzoic acids in cells of V. planifolia.

Journal Article↗
PubMed2003

Role of cytochrome P4501B1 in benzo[a]pyrene bioactivation to DNA-binding metabolites in mouse vascular smooth muscle cells: evidence from 32P-postlabeling for formation of 3-hydroxybenzo[a]pyrene and benzo[a]pyrene-3,6-quinone as major proximate genotoxic intermediates.

Benzo[a]pyrene (BP), a polycylic aromatic hydrocarbon (PAH), is a potent atherogen and carcinogen in laboratory animals. Since genotoxic mechanisms may contribute to the development of atherosclerosis by PAHs, we have tested the hypotheses that: 1) BP induces DNA adducts in mouse aortic smooth muscle cells (SMCs); 2) 3-hydroxybenzo[a]pyrene (3-OH-BP) and benzo[a]pyrene-3,6-quinone (BPQ) are proximate genotoxic metabolites; and 3) cytochrome P4501B1 (CYP1B1) mediates the activation of BP and its metabolites to ultimate genotoxic intermediates. Cultured mouse aortic SMCs were treated with BP, 3-OH-BP, or BPQ for 24 h, and DNA adduct formation was analyzed by (32)P-postlabeling. In some experiments, cells were pretreated with the CYP1B1 inhibitor 1-ethynylpyrene (EP) prior to exposure to BP or its metabolites. BP, 3-OH-BP, and BPQ induced formation of several DNA adducts that were not observed in dimethylsulfoxide-treated cells. Re- and cochromatography experiments indicated that 3-OH-BP and BPQ were proximate genotoxic metabolites of BP. DNA adduct formation was strongly inhibited by EP, a specific inhibitor of CYP1B1. BP treatment of SMCs resulted in induction of aryl hydrocarbon hydroxylase (AHH) activity and CYP1B1, but not CYP1A1, apoprotein. EP also blocked AHH induction by BP. In conclusion, the results of this study support the hypothesis that in SMCs, which are target sites for the development of atherosclerosis, the major bioactivation pathway of BP entails CYP1B1-mediated formation of the 3-OH-BP and BPQ, which are proximate genotoxic metabolites that may in turn get transformed to ultimate DNA-binding metabolites, which may contribute to atherogenesis by PAHs.

Animals↗