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PubMed2006

Theoretical studies on electrochemistry of p-aminophenol.

Geometric parameters, vibrational frequencies and thermochemical values of p-quinonimine (p-Q) and p-aminophenol (p-AP) were computed by ab initio calculation (HF) and density function theory (DFT) with the 6-31G(d,p) basis set. Cyclic voltammetry with a goldren electrode of p-AP solutions in phosphate buffers at pH 7.30 showed that standard electrode potential of half reaction for (p-Q) and (p-AP) is 0.728V. Standard electrode potential of half reaction for p-Q and p-AP were calculated using the sum of electronic and thermal free energies of p-Q and p-AP with normal hydrogen electrode (NHE) as a reference electrode. The results show that the theoretical standard electrode potential of half reaction for p-Q and p-AP is 0.682V at B3LYP/6-31G(d,p) level and 0.622V at HF/6-31G(d,p) level, respectively, indicating that computed standard electrode potential at B3LYP/6-31G(d,p) level are more reliable than that at HF/6-31G(d,p) level.

Aminophenols↗

PubMed2005

Time-dependent effect of p-aminophenol (PAP) toxicity in renal slices and development of oxidative stress.

p-Aminophenol (PAP), a metabolite of acetaminophen, is nephrotoxic. This study investigated PAP-mediated changes as a function of time that occur prior to loss of membrane integrity. Experiments further evaluated the development of oxidative stress by PAP. Renal slices from male Fischer 344 (F344) rats (N = 4-6) were exposed to 0.1, 0.25, and 0.5 mM PAP for 15-120 min under oxygen and constant shaking at 37 degrees C. Pyruvate-stimulated gluconeogenesis, adenine nucleotide levels, and total glutathione (GSH) levels were diminished in a concentration- and time-dependent manner prior to detection of a rise in lactate dehydrogenase (LDH) leakage. Glutathione disulfide (GSSG) levels were increased by PAP suggesting the induction of oxidative stress. Western blot analysis confirmed a rise in 4-hydroxynonenal (4-HNE)-adducted proteins in tissues exposed to 0.1 and 0.25 mM PAP for 90 min. The appearance of 4-HNE-adducted proteins at the 0.1 mM concentration of PAP occurred prior to development of increased LDH leakage. Pretreatment with 1 mM glutathione (GSH) for 30 min only partially reduced PAP toxicity as LDH values were less severely depleted relative to tissues not pretreated with GSH. In contrast, pretreatment for 15 min with 2 mM ascorbic acid completely protected against PAP toxicity. Further studies showed that ascorbic acid pretreatment prevented PAP-mediated depletion of GSH. In summary, PAP rapidly depletes GSH and adenine nucleotides and inhibits gluconeogenesis prior to a rise in LDH leakage. PAP induces oxidative stress as indicated by an increase in GSSG and 4-HNE-adducted proteins. Ascorbic acid pretreatment prevents PAP toxicity by maintaining GSH status.

Adenine Nucleotides↗

PubMed2005

Pyruvate reduces 4-aminophenol in vitro toxicity.

Pyruvate has been observed to reduce the nephrotoxicity of some agents by maintaining glutathione status and preventing lipid peroxidation. This study examined the mechanism for pyruvate protection of p-aminophenol (PAP) nephrotoxicity. Renal cortical slices from male Fischer 344 rats were incubated for 30-120 min with 0, 0.1, 0.25 or 0.5 mM PAP in oxygenated Krebs buffer containing 0 or 10 mM pyruvate or glucose (1.28 or 5.5 mM). LDH leakage was increased above control by 0.25 and 0.5 mM PAP beginning at 60 min and by 0.1 mM PAP at 120 min. Pyruvate prevented an increase in LDH leakage at 60- and 120-min exposure to 0.1 and 0.25 mM PAP. Pyruvate also prevented a decline in ATP levels. Glucose (1.28 and 5.5 mM) provided less protection than pyruvate from PAP toxicity. Total glutathione levels were diminished by 0.1 and 0.25 mM PAP within 60 and 30 min, respectively. Pyruvate prevented the decline in glutathione by 0.1 mM PAP at both time periods and at 30 min for 0.25 mM PAP. Pyruvate reduced the magnitude of glutathione depletion by 0.25 mM PAP following a 60-min incubation. Glutathione disulfide (GSSG) levels in renal slices were increased at 60 min by exposure to 0.25 mM PAP, while pyruvate prevented increased GSSG levels by PAP. Pyruvate also reduced the extent of 4-hydroxynonenal (4-HNE)-adducted proteins present after a 90-min incubation with PAP. These results indicate that pyruvate provided protection for PAP toxicity by providing an energy substrate and reducing oxidative stress.

Aminophenols↗

PubMed2005

Comparison of para-aminophenol cytotoxicity in rat renal epithelial cells and hepatocytes.

Several chemicals, including para-aminophenol (PAP), produce kidney damage in the absence of hepatic damage. Selective nephrotoxicity may be related to the ability of the kidney to reabsorb filtered water, thereby raising the intraluminal concentration of toxicants and exposing tubular epithelial cells to higher concentrations than would be present in other tissues. The present experiments tested the hypothesis that hepatocytes and renal epithelial cells exposed to equivalent concentrations of PAP would be equally susceptible to toxicity. Hepatocytes and renal epithelial cells were prepared by collagenase digestion of tissues obtained from female Sprague-Dawley rats. Toxicity was monitored using trypan blue exclusion, oxygen consumption and ATP content. We measured the rate of PAP clearance and formation of PAP-glutathione conjugate by HPLC. We found that renal epithelial cells accumulated trypan blue and showed declines in oxygen consumption and ATP content at significantly lower concentrations of PAP and at earlier time points than hepatocytes. The half-life of PAP in hepatocyte incubations was significantly shorter (0.71+/-0.07 h) than in renal epithelial cell incubations (1.33+/-0.23 h), suggesting that renal epithelial cells were exposed to PAP for longer time periods than hepatocytes. Renal epithelial cells formed significantly less glutathione conjugates of PAP (PAP-SG) than did hepatocytes, consistent with less efficient detoxification of reactive PAP intermediates by renal epithelial cells. Finally, hepatocytes contained significant more reduced glutathione (NPSH) than did renal epithelial cells, possibly explaining the enhanced formation of PAP-SG by this cell population. In conclusion, our data indicates that renal epithelial cells are intrinsically more susceptible to PAP cytotoxicity than are hepatocytes. This enhanced cytotoxicity may be due to longer exposure to PAP and/or reduced detoxification of reactive intermediates due to lower concentrations of reduced NPSH in renal epithelial cells than in hepatocytes.

Aminophenols↗

PubMed2005

Under the skin: Biotransformation of para-aminophenol and para-phenylenediamine in reconstructed human epidermis and human hepatocytes.

We investigated the biotransformation of the oxidative arylamine (AA) hair dye ingredients [14C]-para-aminophenol (PAP) and [14C]-para-phenylenediamine (PPD) in reconstructed human epidermis and human hepatocytes. Human epidermis quantitatively transformed PAP to its N-acetylated derivative (APAP), whereas hepatocytes transformed PAP to sulfate or glucuronic acid conjugates of APAP or PAP as well as free APAP. Epidermis and hepatocytes converted PPD to N-mono- (MAPPD) and N,N'-di-acetylated (DAPPD) derivatives. At higher concentrations of PPD (250-1000 microM), epidermis or hepatocytes produced more of the MAPPD, whereas concentrations below 250 microM and lower favoured formation of the DAPPD metabolite. When compared with epidermis, human hepatocytes had a three-fold or eight-fold greater capacity for generation of MAPPD or DAPPD, respectively. No evidence of transformation of PAP or PPD to N-hydroxylated derivatives was found in epidermis or hepatocytes. Our results suggest that (i) after dermal absorption of PAP or PPD, humans are systemically exposed to acetylated derivatives; (ii) current in vitro skin absorption studies may be inadapated for determination of human systemic exposure to AAs due to reduced or absent metabolic capacity of non-viable skin; (iii) due to qualitative differences between dermal and hepatic metabolism, oral toxicity studies may be unsuited for the hazard assessment of dermal exposure to AAs; and (iv) use of induced rodent liver S9 metabolic activation systems for in vitro genotoxicity studies may produce misleading results on the hazard of human dermal exposure to AAs. In conclusion, our data support the growing evidence that AAs are transformed in human skin and suggest that current practices of safety assessment of AAs should take these findings into account.

Aminophenols↗

PubMed2006

p-Aminophenol degradation by ozonation combined with sonolysis: operating conditions influence and mechanism.

The degradation of p-aminophenol (PAP) in aqueous solution by sonolysis, by ozonation, and by a combination of both was investigated in laboratory-scale experiments. Operation parameters such as pH, temperature, ultrasonic energy density and ozone dose were optimized with regard to the efficiency of PAP removal. The concentration of PAP during the reaction was detected by high-pressure liquid chromatography. The concentrations of ammonium ions and nitrate ions were monitored during the degradation. Intermediate products such as 4-iminocyclohexa-2,5-dien-1-one, phenol, but-2-enedioic acid, and acetic acid were detected by gas chromatography coupled with mass spectrometry. The degradation rate of PAP was higher in the combined system than in the linear combination of separate experiments. The degradation efficiency was decreased rapidly when n-butanol was added to the combined reaction system, which showed that some radical reaction might proceed during the laboratory experiments.

Aminophenols↗

PubMed2004

Flow injection determination of p-aminophenol at trace level using inhibited luminol-dimethylsulfoxide-NaOH-EDTA chemiluminescence.

A novel flow injection procedure was developed for the determination of p-aminophenol (PAP) based on the inhibition by PAP of the chemiluminescence from luminol-dimethylsulfoxide (DMSO)-NaOH-EDTA system. The method has merits of higher sensitivity, wider linear range, simpler procedure, and a more rapid analyzing speed. It is applicable for the determination of PAP in the range of 2.5 x 10(-10)-5.0 x 10(-8) g mL(-1) with a detection limit of 1.9 x 10(-10) g mL(-1). The relative standard deviation (RSD) for 5.0 x 10(-9) g mL(-1) PAP is 0.78% (n=15). The method has been successfully used to determine PAP in industrial wastewaters and environmental waters. Additionally, the inhibition mechanism was also discussed briefly.

Aminophenols↗

PubMed2002

Spectrophotometric determination of folic acid in pharmaceutical preparations by coupling reactions with iminodibenzyl or 3-aminophenol or sodium molybdate-pyrocatechol.

Novel coupling reagents are used for the simple and sensitive spectrophotometric determination of folic acid either in pure form or in its pharmaceutical preparations. The methods are based on the probable diazotization of the p-aminobenzoylglutamic acid obtained after reductive clevage of folic acid, followed by either coupling with iminodibenzyl to give a violet product with lambda(max) of 580nm or coupling with 3-aminophenol to produce an orange yellow-colored product with lambda(max) of 460nm. Sodium molybdate and pyrocatechol are used in the third method and the pale red-colored product formed has a lambda(max) of 490nm. The methods are highly reproducible and have been applied to the determination of folic acid in tablets and the results compare favorably with the official method. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed methods.

Aminophenols↗

PubMed2003

3-Aminophenol as a novel coupling agent for the spectrophotometric determination of sulfonamide derivatives.

A rapid, simple and sensitive spectrophotometric method for the determination of some sulfa drugs is described. The method is based on the formation of orange yellow colored azo product by the diazotization of sulfonamides, viz., dapsone (DAP), sulfathiazole (SFT), sulfadiazine (SFD), sulfacetamide (SFA), sulfamethoxazole (SFMx), sulfamerazine (SFMr), sulfaguanidine (SFG) and sulfadimidine (SFDd) followed by a coupling reaction with 3-aminophenol in aqueous medium. Absorbance of the resulting orange yellow product is measured at 460 nm and is stable for 6 days at 27 degrees C. Beer's law is obeyed in the concentration range of 0.05-8.0 microg/ml at the wavelength of maximum absorption. The method is successfully employed for the determination of sulfonamides in various pharmaceutical preparations and common excipients used as additives in pharmaceuticals do not interfere in the proposed method. Plausible reaction mechanism is proposed for the formation of the azo product.

Aminophenols↗

PubMed2000

Effect of antioxidants on para-aminophenol-induced toxicity in LLC-PK1 cells.

The present studies were designed to investigate the susceptibility of LLC-PK1 cells to cytotoxicity induced by para-aminophenol (PAP) and the ability of antioxidants to prevent PAP-induced cytotoxicity. LLC-PK1 cells were incubated for 4 h with varying concentrations of PAP (0-0.2 mM). Incubation was continued for 20 h and viability was monitored at 24 h after initial exposure to PAP. For coincubation experiments, cells were incubated for 4 h with various antioxidants [including ascorbate, glutathione (GSH), butylated hydroxytoluene (BHT), beta-nicotinamide adenine dinucleotide (NADH), or beta-nicotinamide adenine dinucleotide phosphate (NADPH)] in the absence or presence of 0.1 mM PAP. For preincubation experiments, cells were incubated for 1 h with ascorbate, GSH or NADPH. Antioxidants were removed and cells were exposed to 0 or 0.1 mM PAP for 4 h. Viability was determined 24 h following PAP exposure. LLC-PK1 cells displayed a steep concentration-response relationship for PAP; 0.1 mM PAP caused approximately 50% loss of viability. Coincubation with ascorbate, GSH and NADPH was without effect on cell viability in the absence of PAP and attenuated PAP-induced losses in viability. In contrast, NADH was ineffective in preventing PAP-induced cytotoxicity. BHT alone produced a significant loss of cell viability and was ineffective in preventing PAP cytotoxicity. Inability of NADH to prevent PAP-induced cytotoxicity was related to rapid degradation of NADH in aqueous solution. Preincubation of cells with ascorbate or GSH but not NADPH was associated with attenuation of PAP-induced cytotoxicity. These data suggest that (1) PAP is cytotoxic to LLC-PK1 cells, (2) a portion of PAP cytotoxicity is due to nonenzymatic oxidation that occurs in the incubation medium, and (3) a portion of PAP cytotoxicity is due to enzymatic or nonenzymatic oxidation that occurs within cells.

Aminophenols↗

PubMed2000

Lipoxygenase-mediated biotransformation of p-aminophenol in the presence of glutathione: possible conjugate formation.

This study tested a hypothesis that soybean lipoxygenase (SLO), a model enzyme, may be capable of generating a glutathione (GSH) conjugate(s) from p-aminophenol (PAP). Horseradish peroxidase was employed as a positive control. GSH depletion or an increase in the absorption at 327 nm with time due to GS-PAP formation was used to quantitate the reaction. The rate of GS-PAP formation was dependent on the incubation time and the amount of SLO and exhibited Km values of 0.44 and 0.71 mM for PAP and H2O2, respectively. Classical inhibitors of lipoxygenase and free radical scavengers markedly decreased the rate of GS-PAP formation in a concentration-dependent manner. PAP-dependent GSH depletion from the reaction medium occurred at a rate of 2.37 +/- 0.18 micromol/min/mg protein. Collectively, the results suggest that lipoxygenase pathway may be involved in the enzymatic formation of GSH conjugate(s) from PAP.

Aminophenols↗

PubMed1998

Mutagenicity of p-aminophenol in E. coli WP2uvrA/pKM101 and its relevance to oxidative DNA damage.

It was recently reported that p-aminophenol (p-AP) induces DNA cleavage in mouse lymphoma cells, CHO cells and human lymphoblastoid cells. The mutagenicity of p-AP has not, however, been detected by reverse mutation assays. The purpose of this study was to assess the mutagenicity of p-AP by reverse mutation assay using Escherichia coli WP2uvrA/pKM101, which has a spectrum for detecting mutations different from those of other strains in the family with an AT base pair at the mutation site and has higher sensitivity to certain oxidative mutagens as compared to other strains. We found that p-AP was mutagenic to E. coli WP2uvrA/pKM101. The mutagenic activity of this compound was suppressed with the addition of dimethylsulfoxide or catalase, suggesting the involvement of active oxygen species in the mutagenic process induced by p-AP. To further elucidate the underlying mechanism, we used isolated DNA for the following experiments. It was revealed, by gel electrophoretic analysis, that p-AP induced DNA cleavage in the presence of Fe(III). However, p-AP alone did not induce this cleavage. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by p-AP in calf thymus DNA was also detected in the presence of Fe(III) by HPLC with an electrochemical detector. ESR-spin trapping experiments using DMPO detected the production of hydroxyl radical (.OH) in the solution of p-AP with Fe(III). Both p-AP mediated DNA damages and .OH production by p-AP in the presence of Fe(III) were completely inhibited by .OH scavengers (ethanol, mannitol, sodium formate, dimethylsulfoxide) and catalase. These results suggest that .OH derived from the reaction between H2O2 and Fe(III) (Fenton reaction) participates in the oxidative DNA damage. Accordingly, the same mechanism might be working in E. coli WP2uvrA/pKM101 during induction of the mutation by p-AP.

Adenosine Triphosphatases↗

PubMed2000

Application of aluminium(III) complex with salicylidene-o-aminophenol to the fluorometric determination of nucleic acids.

In buffer medium of hexamethylene tetraamine-HCl at pH 5.9 the aluminium(III) complex with salicylidene-o-aminophenol (SAP) has a fluorescence peak at 508 nm with excitation at 410 nm. When nucleic acid coexists, it reacts with the complex within 8 min at room temperature to produce a non-fluorescent product, resulting in the decrease of fluorescence intensity of the aluminium complex. On basis of this, a new fluorometric method for nucleic acids determination is proposed. The calibration graphs for calf thymus DNA, fish sperm DNA and yeast RNA are linear up to 5.0, 4.0 and 3.0 microg ml(-1), respectively, and corresponding detection limits are 49, 52 and 62 ng ml(-1). The synthetic samples are analyzed with relative standard deviation of five measurements of 3.9-6.0%. DNA in an extraction product from human blood is determined using the calibration graph for calf thymus DNA, and the result is very close to that by the ethidium bromide assay. Compared with some established fluorometric methods, this procedure is sensitive, selective, reliable, reproducible and practical. The association constant of calf thymus DNA with the complex is estimated by two graphic methods. It is suggested that the binding reaction between nucleic acids with the complex proceeds in an intercalation way.

Alum Compounds↗

PubMed1993

Small-volume voltammetric detection of 4-aminophenol with interdigitated array electrodes and its application to electrochemical enzyme immunoassay.

A small-volume voltammetric detection of 4-aminophenol (PAP) has been developed using an interdigitated array (IDA) microelectrode cell in order to apply the IDA to electrochemical enzyme immunoassay. The signal of PAP at the IDA was steady state, and its magnitude was amplified compared with that of the usual single electrode due to redox cycling of PAP between the two finger sets of the IDA. A linear relationship between PAP concentration and cathodic limiting current was obtained from 1 to 1000 microM, reproducibly. The minimum sample volume in the measurement was reduced to 800 nL. High sample throughput of less than 1-min detection time per sample was achieved on 2-10-microL PAP samples. This IDA cell was applied to the electrochemical enzyme immunoassay of mouse IgG. Alkaline phosphatase was used as the enzyme label. The mouse IgG concentration was evaluated by detecting the concentration of PAP, which is the product of enzymatic reaction of the substrate, 4-aminophenyl phosphate (PAPP). Anti-mouse IgG was covalently immobilized on the glass surface of the small-volume immunowells by carbodiimide coupling. The assay range was 10-1000 ng/mL using 10-microL sample and 20-microL substrate solutions.

Alkaline Phosphatase↗

PubMed2004

Charge redistribution on electronic excitation. Dipole moments of cis- and trans-3-aminophenol in their S(0) and S(1) electronic states.

Rotationally resolved electronic spectroscopy in the gas phase, in the absence and presence of an applied electric field, has been used to distinguish the two conformers of 3-aminophenol (3AP) on the basis of differences in their electric dipole moments. cis-3AP has micro = 2.3 D, and trans-3AP has micro = 0.7 D, in their ground electronic states. The two observed values are approximately equal to those expected on the basis of bond dipole additivity rules. However, these rules fail to predict the large change in both the magnitude and the orientation of micro when the two conformers of 3AP absorb light. cis-3AP has micro = 3.3 D, and trans-3AP has micro = 1.7 D, in their excited S(1) electronic states; the angles of orientation of micro with respect to the a inertial axis change by 13 degrees and 38 degrees, respectively. This effect is attributed to (1)L(b)/(1)L(a) state mixing in the S(1) state.

Aminophenols↗

PubMed1994

Synthesis and topical antiinflammatory and antiallergic activities of antioxidant o-aminophenol derivatives.

In order to develop novel compounds for topical use possessing antiallergic as well as antiinflammatory activities, a series of o-aminophenol derivatives bearing H1-antihistaminic structures were synthesized and their effects were investigated on lipid peroxidation in rat brain homogenates, antiinflammatory effection arachidonic acid- and 12-O-tetradecanoylphorbol-13- acetate-induced mouse ear edema and antiallergic effect on 48-h homologous passive cutaneous anaphylaxis in rats. Furthermore, the effects of these compounds on delayed-type hypersensitivity reaction in mice were examined. Several N-monosubstituted amino-4-methylphenols were found to exert potent inhibitory activities in all of these assays. Of these compounds, 4m was chosen for further development as AD0261.

Administration, Topical↗

PubMed1992

Flow injection electrochemical enzyme immunoassay for theophylline using a protein A immunoreactor and p-aminophenyl phosphate-p-aminophenol as the detection system.

A competitive electrochemical enzyme immunoassay has been developed for the antiasthmatic drug theophylline, utilizing a controlled-pore glass-protein A immunoreactor and flow injection techniques. p-Aminophenyl phosphate, a substrate for alkaline phosphatase, has been used in this assay, and its hydrolysis product p-aminophenol was determined at +0.2 V versus the saturated calomel electrode. For each sample the antibody-protein A reaction takes place at near-neutral pH, and the complexes are eluted at acid pH. Serum theophylline has been determined by this method, and good relative standard deviations and percentage recoveries have been achieved.

Alkaline Phosphatase↗

PubMed2002

Determination of 4-aminophenol using the quartz crystal microbalance sensor.

In this paper we report a method for the determination of 4-aminophenol (4-AP) in solution using a quartz crystal microbalance (QCM) sensor. 4-AP reacts with (para-unsubstituted) phenols to form hydrophobic indophenol dye species that precipitate out and adsorb to the surface of the crystal to produce a shift in the crystal resonant frequency. This frequency change, due to in-situ indophenol mass adsorption, can be related to the initial 4-AP concentration. A range of phenols (namely o-cresol, 1-naphthol, resorcinol, catechol and 8-hydroxyquinoline) and their reaction with 4-AP were tested. Ammonium persulfate (APS) and potassium periodate were used as initiators to improve the speed of the reaction and the rate of formation of the precipitate. APS elicited improved signal in terms of response times and frequency shifts compared with KIO4. Of the phenols studied, resorcinol gave the best response time of 6 min for 4-AP determination. The reaction of resorcinol with 4-AP gave extended response times and signal size with decreasing concentration of 4-AP (in the range 2-5 mM).

Aminophenols↗