Insight into multicopper oxidase laccase from Myrothecium verrucaria ITCC-8447: a case study using in silico and experimental analysis

The oxidation activity of multicopper-oxidases overlaps with different substrates of laccases and bilirubin oxidases, thus in the present study an integrated approach of bioinformatics using homology modeling, docking, and experimental validation was used to confirm the type of multicopper-oxidase in Myrothecium verrucaria ITCC-8447. The result of peptide sequence of M. verrucaria ITCC-8447 enabled to predict the 3 D-structure of multicopper-oxidase. It was overlapped with the structure of laccase and root mean square deviation (RMSD) was 1.53 Å for 533 and, 171 residues. The low binding energy with azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) (-5.64) as compared to bilirubin (-4.39) suggested that M. verrucaria ITCC-8447 have laccase-like activity. The experimental analysis confirmed high activity with laccase specific substrates, phenol (18.3 U/L), ampyrone (172.4 U/L) and, ampyrone phenol coupling (50 U/L) as compared to bilirubin oxidase substrate bilirubin (16.6 U/L). In addition, lowest binding energy with ABTS (-5.64), syringaldazine SYZ (-4.83), guaiacol GCL (-4.42), and 2,6-dimethoxyphenol DMP (-4.41) confirmed the presence of laccase. Further, complete remediation of two hazardous model pollutants i.e., phenol and resorcinol (1.5 mM) after 12 h of incubation and low binding energy of -4.32 and, -4.85 respectively confirmed its removal by laccase. The results confirmed the presence of laccase in M. verrucaria ITCC-8447 and its effective bioremediation potential.

Exploring DNA binding and nucleolytic activity of few 4-aminoantipyrine based amino acid Schiff base complexes: a comparative approach

A series of novel Co(II), Cu(II), Ni(II) and Zn(II) complexes were synthesized from Schiff base(s), obtained by the condensation of 4-aminoantipyrine with furfural and amino acid (glycine(L1)/alanine(L2)/valine(L3)) and respective metal(II) chloride. Their structural features and other properties were explored from the analytical and spectral methods. The binding behaviors of the complexes to calf thymus DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. The intrinsic binding constants for the above synthesized complexes are found to be in the order of 10(2) to 10(5) indicating that most of the synthesized complexes are good intercalators. The binding constant values (Kb) clearly indicate that valine Schiff-base complexes have more intercalating ability than alanine and glycine Schiff-base complexes. The results indicate that the complexes bind to DNA through intercalation and act as efficient cleaving agents. The in vitro antibacterial and antifungal assay indicates that these complexes are good antimicrobial agents against various pathogens. The IC50 values of [Ni(L1)2] and [Zn(L1)2] complexes imply that these complexes have preferable ability to scavenge hydroxyl radical.

Binding and conformational changes of human serum albumin upon interaction with 4-aminoantipyrine studied by spectroscopic methods and cyclic voltammetry

The interactions of 4-aminoantipyrine (AAP) with human serum albumin (HSA) have been studied by UV-visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. The binding of 4-aminoantipyrine quenches the HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 10(5) M(-1). The experimental results showed that AAP effectively quenched the intrinsic fluorescence of HSA via dynamic type of quenching. In addition, according to the synchronous fluorescence spectra of HSA in presence of 4-aminoantipyrine, the tryptophan residue of the proteins are most perturbed by the binding process. The number of binding sites, the binding constant, site probe study, some common metal ions effect and the thermodynamic parameters were calculated.

DNA binding mode of novel tetradentate amino acid based 2-hydroxybenzylidene-4-aminoantipyrine complexes

Few transition metal complexes of tetradentate N(2)O(2) donor Schiff base ligands containing 2-hydroxybenzylidene-4-aminoantipyrine and amino acids (alanine/valine) abbreviated to KHL(1)/KHL(2) have been synthesized. All the metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The Schiff bases KHL(1)/KHL(2) are found to act as tetradentate ligands using N(2)O(2) donor set of atoms leading to a square-planar geometry for the complexes around the metal ions. The binding behaviors of the complexes to calf thymus DNA have been investigated by absorption spectra, viscosity measurements and cyclic voltammetry. The DNA binding constants reveal that all these complexes interact with DNA through minor groove binding mode. The studies on mechanism of photocleavage reveal that singlet oxygen ((1)O(2)) and superoxide anion radical (O(2)(-)) may play an important role in the photocleavage. The Schiff bases and their metal complexes have been screened for their in vitro antibacterial activities against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, Klebsiella pneumoniae and antifungal activities against Aspergillus niger, Fusarium solani, Culvularia lunata, Rhizoctonia bataicola and Candida albicans by MIC method.

[Effect of herbicide tralkoxydim and 2-acylcyclohexane-1,3-diones on peroxidase activity]

Effect of 2-acylcyclohexane-1,3-dione derivatives (tralkoxydim and its diketone precursors) on peroxidase-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), o-phenylenediamine (PDA), and the phenol-4-aminoantipyrine (4-AAP) couple has been studied. This effect varies from horseradish peroxidase (HRP) inactivation to activation in the reactions of peroxidation ofTMB, PDA, and, to a lesser extent, the phenol-4-AAP couple. The diketone-mediated HRP activation depends strongly on pH, presence of dimethylformamide, the structures of tralkoxydim and other diketones, and the substrate nature. The type of activation in the course of peroxidation with the presence of tralkoxydim can be noncompetitive (PDA and TMB) or mixed (TMB) depending on conditions. The maximal level of the HRP activation mediated by diketones depends on their structure. It can reach 4000% of the initial HRP-catalyzed peroxidation rate for TMB and ca. 1000% for PDA. A test system is proposed for quantitative tralkoxydim assay at millimolar concentration. It includes HRP and TMB as the substrate with spectrometrical monitoring of the TMB peroxidation product at 655 nm.

Inhibition of cyclooxygenases by dipyrone

BACKGROUND AND PURPOSE

Dipyrone is a potent analgesic drug that has been demonstrated to inhibit cyclooxygenase (COX). In contrast to classical COX-inhibitors, such as aspirin-like drugs, dipyrone has no anti-inflammatory effect and a low gastrointestinal toxicity, indicating a different mode of action. Here, we aimed to investigate the effects of dipyrone on COX.

EXPERIMENTAL APPROACH

The four major metabolites of dipyrone, including the two pharmacologically active metabolites, 4-methyl-amino-antipyrine (MAA) and amino-antipyrine (AA), were used to characterise their binding to COX and haem as well as their effects on the biochemical properties of COX. Mass spectrometry, UV and visible photometry were used to study binding and prostaglandin production. Levels of anti-oxidant enzymes were assessed by Western blotting.

KEY RESULTS

The pharmacologically active metabolites of dipyrone, MAA and AA, did not inhibit COX activity in vitro like classical COX inhibitors, but instead redirected the prostaglandin synthesis, ruling out inhibition of COX through binding to its active site. We found that MAA and AA formed stable complexes with haem and reacted with hydrogen peroxide in presence of haem, ferrous ions (Fe(2+)) or COX. Moreover, MAA reduced Fe(3+) to Fe(2+) and accordingly increased lipid peroxidation and the expression of anti-oxidant enzymes in cultured cells and in vivo.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that the pharmacologically active metabolites of dipyrone inhibit COX activity by sequestering radicals which initiate the catalytic activity of this enzyme or through the reduction of the oxidative states of the COX protein.

Extracellular peroxidase production by Coprinus species from urea-treated soil

Thirteen strains of inky-cap mushroom Coprinus species were evaluated for the production of extracellular peroxidase. The liquid fermentation was carried out in shake flasks containing 1% glucose, 0.5% peptone, 0.3% yeast extract, and 0.3% malt extract broth at 25 °C. Peroxidase activity was detected in the liquid culture of several Coprinus species, including C. echinosporus NBRC 30630; C. macrocephalus NBRC 30117; Coprinus spp. UAMH 10065, UAMH 10066, UAMH 10067, and 074, after 10 days of growth. Peroxidase production by Coprinus sp. UAMH 10067, a Coprinus species isolated from urea-treated soil, was comparable to that of C. cinereus and reached 15 U·mL–1 after 10 days. In addition, the peroxidase from Coprinus sp. UAMH 10067 was apparently more thermally stable than the enzyme produced by C. cinereus.Key words: Coprinus species, urea treatment, phenol, wastewater treatment.

Catalytic spectrofluorimetric determination of superoxide anion radical and superoxide dismutase activity using N,N-dimethylaniline as the substrate for horseradish peroxidase (HRP)

The coupled reaction of N,N-dimethylaniline (DMA) with 4-aminoantipyrine (4-AAP) using superoxide anion radical (O2-) as oxidizing agent under the catalysis of horseradish peroxidase (HRP) was studied. Based on the reaction, O2- produced by irradiating Vitamin B2, (VB2) was spectrophotometricly determined at 554 nm. The linear range of this method was 1.8 x 10(-6)-1.2 x 10(-4) mol l(-1) with a detection limit of 5.3 x 10(-7) mol l(-1). The effect of interferences on the determination of O2- was investigated. The proposed method was successfully applied to the determination of superoxide dismutase (SOD) activity in human blood and mouse blood.

[Co-oxidation of phenols and 4-aminoantipyrene catalyzed by microperoxidase and their complexes with proteins]

The kinetic parameters of 4-aminoantipyrine (AAP) co-oxidation with phenol or p-iodophenol in a wide range of hydrogen peroxide concentrations were compared for microperoxidases MP-8, MP-9, MP-11, horseradish peroxidase (HRP) and peroxidase of Arthromyces ramosus (PAR). The peroxidatic activity increased in the following order: HRP > PAR > MP-9 > MP-8 > MP-11. Microperoxidase complexes with human serum albumin (1:1) retained their peroxidatic activity at high H2O2 concentrations, protecting haem from destruction by active radicals. Monoclonal antibodies against porphyrin decreased the peroxidatic activities of three microperoxidases during co-oxidation of AAP and phenol and protected haem. Inert proteins (BSA, ovalbumin) had little effect on the HRP activity, whereas enzyme-specific antibodies strongly activated HRP at high concentrations of hydrogen peroxide, thereby forming an immune complex protecting HRP from its dissociation down to haem and the apoenzyme.

Enzymatic measurement of phosphatidylglycerol in amniotic fluid

We describe an enzymatic method for measuring phosphatidylglycerol (PG) at concentrations as low as 0.2 mumol/L in amniotic fluid. Amniotic fluid (1.5 mL) is centrifuged at 10,000g for 20 min to obtain a lamellar body pellet, which is reconstituted with 0.5 mL of buffer. The PG is measured by a two-step enzymatic scheme. Recovery studies demonstrated that the pellet contains > 97% of the PG present in amniotic fluid. Between-run CVs were 28%, 5.7%, and 2.6% for amniotic fluid controls with means of 0.32, 3.9, and 10.7 mumol/L, respectively (n = 20). The enzymatic procedure was not significantly affected by blood, meconium, bilirubin, or other phospholipids. Lecithin/sphingomyelin ratio (n = 101) and fluorescence polarization (n = 127) compared with log(PG) showed correlation coefficients of 0.832 and -0.866, respectively. This test's ability to detect low concentrations of PG in amniotic fluid may make it a better predictor of fetal lung immaturity than previous methods.

Interaction of myeloperoxidase and elastase enzyme activity with the antihypertensive agents hydralazine and dihydralazine

Autoantibodies directed against myeloperoxidase and elastase have been found in patients developing hydralazine-induced lupus and hydralazine-induced isolated glomerulonephritis. The aim of this study was to investigate influence of hydralazine and dihydralazine upon myeloperoxidase and elastase enzyme activity. Using a 4-aminoantipyrin in vitro system, dihydralazine was 2.5 times as potent in inhibiting myeloperoxidase activity as compared to hydralazine. The corresponding Ki-values were 4 microns M for dihydralazine and 25 microM for hydralazine. When using 2.2'-azino-bis-3-ethyl-benzothiazoline-6-sulphonic acid system inhibition was found at lower concentrations. Furthermore, the difference between the compounds was not so pronounced as seen for 4-aminoantipyrin. The Ki-values for hydralazine and dihydralazine were 1.2 and 1.4 microM respectively. Complete inhibition was seen for both compounds at concentrations above 7.5 microM. Hydralazine binds to elastase, but neither hydralazine nor dihydralazine inhibited elastase enzyme activity.

Formation and excretion of dipyrone metabolites in man

The formation and urinary excretion of the dipyrone metabolites, methylaminoantipyrine (MAA), aminoantipyrine (AA), formylaminoantipyrine (FAA) and acetylaminoantipyrine (AAA) were determined following administration of a single oral 1.0 g dose of dipyrone to 12 healthy volunteers. The AAA/AA plasma ratio showed that 3 subjects were slow and 9 were rapid acetylators. Pharmacokinetic parameters were determined separately for each group. A good correlation was found between the plasma and urine AAA/AA ratios. The renal clearance of the four metabolites was similar for both phenotypes. A significant difference in the rate of formation of dipyrone metabolites was found for AA, 0.25 (slow) vs 0.1 ml.min-1.kg-1 (rapid), and for AAA 0.75 (slow) vs 7.53 ml.min-1.kg-1 (rapid). There were comparable differences between slow and rapid acetylators in the AUC and the urinary excretion extrapolated to infinity for AA and AAA. The present results show that the kinetics of dipyrone metabolites in plasma and urine can provide a useful measure of the activity of the enzymes involved in their production.

Oxidation of hydroquinone by both cellular and extracellular grapevine peroxidase fractions

The oxidation of hydroquinone by two peroxidase (EC 1.11.1.7) fractions obtained from the cells and spent medium of cell cultures of grapevine (Vitis vinifera cv Monastrell) has been studied, and their comparative efficacy (kcat/KM ratio) studied in both the H2O2-consuming and hydroquinone-consuming reactions. While the efficacy in the H2O2-consuming reaction is practically identical for both enzyme fractions, the cellular peroxidase has five-fold more efficacy in the hydroquinone-consuming reaction than the peroxidase located in the spent medium. Screening of cellular peroxidases capable of oxidizing hydroquinone on polyacrylamide gels, by means of a staining reaction based on the nucleophilic attack of 4-aminoantipyrine on p-benzoquinone in acidic media, reveals that all the cellular peroxidase isoenzymes are capable of oxidizing hydroquinone, probably yielding a quinone-diimine as a product of the staining reaction. Since isoperoxidases found in cellular fractions are also present in the spent medium, the values found for the different efficacies in the hydroquinone-consuming reaction must be considered as the results of the different proportions in which each peroxidase isoenzyme was found in the two fractions. The localization of a benzoquinone-generating system of high efficacy inside the plant cell, and probably located in vacuoles, is discussed with respect to the harmful role which the quinone/semiquinone pair might play in cell death, as part of the hypersensitive response expressed within the mechanism of plant disease resistance.

Cytochrome c-catalyzed oxidation of organic molecules by hydrogen peroxide

Cytochrome c catalyzed the oxidation of various electron donors in the presence of hydrogen peroxide (H2O2), including 2-2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 4-aminoantipyrine (4-AP), and luminol. With ferrocytochrome c, oxidation reactions were preceded by a lag phase corresponding to the H2O2-mediated oxidation of cytochrome c to the ferric state; no lag phase was observed with ferricytochrome c. However, brief preincubation of ferricytochrome c with H2O2 increased its catalytic activity prior to progressive inactivation and degradation. Superoxide (O2-) and hydroxyl radical (.OH) were not involved in this catalytic activity, since it was not sensitive to superoxide dismutase (SOD) or mannitol. Free iron released from the heme did not play a role in the oxidative reactions as concluded from the lack of effect of diethylenetriaminepentaacetic acid. Uric acid and tryptophan inhibited the oxidation of ABTS, stimulation of luminol chemiluminescence, and inactivation of cytochrome c. Our results are consistent with an initial activation of cytochrome c by H2O2 to a catalytically more active species in which a high oxidation state of an oxo-heme complex mediates the oxidative reactions. The lack of SOD effect on cytochrome c-catalyzed, H2O2-dependent luminol chemiluminescence supports a mechanism of chemiexcitation whereby a luminol endoperoxide is formed by direct reaction of H2O2 with an oxidized luminol molecule, either luminol radical or luminol diazoquinone.

Zymographic screening of plant peroxidase isoenzymes oxidizing 4-hydroxystilbenes

A zymographic assay is described for the detection of peroxidase isoenzymes oxidizing 4-hydroxystilbene following isoelectric focusing. The assay is based on coupling intermediate products of the oxidation of 4-hydroxystilbene with 4-aminoantipyrine, with resultant formation of dye complexes. Control experiments in the absence of 4-hydroxystilbene and hydrogen peroxide demonstrate the peroxidative nature of the 4-hydroxystilbene-dependent dye reaction.

Antioxidant characteristics of some potential anticataract agents. Studies of aspirin, paracetamol, and bendazac provide support for an oxidative component of cataract

It is conceivable that drugs with anticataract potential possess antioxidant activity. Using defined chelating agents and reducing agents in a number of assays for antioxidant activity, we have demonstrated that paracetamol, aspirin, bendazac, and its metabolite 5-hydroxybendazac possess substantial reducing and/or metal-chelating activity. We found that paracetamol and 5-hydroxybendazac reduced the diphenylpicrylhydrazyl free radical; inhibited butyl peroxide-induced erythrocyte lysis as well as the haematin-catalyzed oxidative coupling of 4-aminoantipyrine and phenol by butyl peroxide. Furthermore, paracetamol, bendazac, and aspirin competed with 3-(2-pyridyl)-5,6-Diphenyl-1,2,4-triazine-4', 4"-disulphonic acid (ferrozine) for ferrous ion.

Aminopyrine metabolism by multiple forms of cytochrome P-450 from rat liver microsomes: simultaneous quantitation of four aminopyrine metabolites by high-performance liquid chromatography

Four aminopyrine metabolites generated by hepatic microsomes were simultaneously assayed by high-performance liquid chromatography. The metabolites were 4-monomethylaminoantipyrine (MAA), 4-aminoantipyrine (AA), 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazoline-5-one (AM-OH), and one unidentified metabolite. MAA was the major metabolite generated by the microsomes; its formation was induced by phenobarbital but not by 3-methylcholanthrene. Female rats had lower N-demethylation activity of aminopyrine than male rats. The production of AA by microsomes was low. The formation of AM-OH was strongly induced by phenobarbital, but treatment with 3-methylcholanthrene reduced its formation. These differences in the microsomal aminopyrine monooxygenase activity are dependent on the relative amounts of the individual cytochrome P-450 isozymes. Therefore, we examined aminopyrine metabolism in a reconstituted system with purified cytochrome P-450s. P-450 UT-2 (P-450h) had high aminopyrine N-demethylation and hydroxylation activities, but P-450 F-2 (P-450i) had low N-demethylation activity and no hydroxylation activities, but P-450 F-2 (P-450i) had low N-demethylation activity and no hydroxylation activity. P-450 PB-4 (P-450b) and P-450 PB-5 (P-450e) had high aminopyrine hydroxylation activity and their N-demethylation activity also was high. The 3-methylcholanthrene-inducible forms P-450 MC-1 (P-450d) and MC-5 (P-450c) had aminopyrine N-demethylation activity but no hydroxylation activity. P-450 UT-4 (RLM2) is a unique form that produced a large amount of the unknown metabolite. P-450 UT-7 had the highest N-demethylation activity. Addition of cytochrome b5 to the reconstituted system enhanced the aminopyrine hydroxylation activities of P-450s UT-1, UT-2, PB-2, and PB-5. Also, the N-demethylation activities of P-450s UT-1, PB-1, PB-2, and MC-1 were increased by cytochrome b5. Metyrapone inhibited the catalytic activities of P-450s PB-4, PB-5, MC-1, and MC-5, and especially those of P-450s UT-4, and UT-7. The kinetics of the four major cytochrome P-450s (P-450 UT-2, UT-4, PB-4, and MC-5) for aminopyrine N-demethylation and hydroxylation activities were studied. P-450s PB-4 and UT-2 had similar Km values (0.50 and 0.62 mM, respectively) in aminopyrine N-demethylation activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose-dependent pharmacokinetics of metabolites of dipyrone in saliva

Metabolites of dipyrone have been determined in the saliva of 18 volunteers following the oral intake of 0.5 g, 1.0 g, 1.5 g, 2.0 g and 2.5 g dipyrone. High concentrations were measured for N-methyl-aminoantipyrine (MAA), the other analgetic active metabolite, 4-aminoantipyrine was found in minor quantities only. N-formyl-antipyrine was not present in the saliva of some volunteers after low doses but could be determined following the intake of doses from 1.5 g - 2.5 g in saliva of all volunteers. N-acetyl-antipyrine appears late in saliva, acetylation rates varied greatly interindividually. Concentrations of the metabolites in saliva mimic the respective non-protein bound fraction in plasma found by other authors.

[Characteristics of induced aminopyrine N-demethylase]

The study of the inducing effect of phenobarbital on the activity of N-demethylase of aminopyrine in the rat liver microsomes revealed the correlation of the rate of enzymic reaction with the changes in the maximum binding of aminopyrine by cytochrome P-450 rather than with the content of hemoprotein itself. The comparison of the activity of N-demethylation of aminopyrine in control and phenobarbital-induced rats showed the quantitative correspondence of the yield of products of the reaction--formaldehyde in the liver microsomes and 4-aminoantipyrine in the urine samples. Self-induction of N-demethylating activity at repeated aminopyrine administration to rats and the dose dependence of this phenomenon were found.

[The influence of chronic renal insufficiency on the demethylating activities of various cytochrome P-450 subspecies in humans]

Caffeine is mainly metabolized by 3-methylcholanthrene-inducible cytochrome P-450 (P-450MC) and metamizol (noramidopyrine methanesulfonate sodium) is mainly metabolized by phenobarbital-inducible cytochrome P-450 (P-450PB). That's why the half life of caffeine and the elimination of the main metabolites of metamizol were used as parameters in vivo characterizing both groups of the cytochrome P-450-complex. The influence of chronic renal insufficiency was investigated (8 patients in the stage of compensated retention, creatinine in serum 380-1280 mumol X l-1, and 6 hemodialyzed patients, here only metamizol elimination was established). Both the caffeine and the metamizol eliminations of patients with chronic renal insufficiency are not different from those of healthy volunteers. We concluded that the demethylation activity of the cytochrome P-450-complex is not distinctly influenced by chronic renal insufficiency.

Determination of serum triglycerides by an accurate enzymatic method not affected by free glycerol

In this automated single-run enzymatic procedure for specific determination of triglycerides in serum, free glycerol is removed from the reaction mixture by pre-incubation with glycerol phosphate oxidase and peroxidase. The subsequent addition of lipase and the chromogen, 4-aminoantipyrine, results in the formation of color proportional to the amount of triglycerides in serum. Standards containing triolein in aqueous detergent are used to calibrate the method. For serum pools from the Centers for Disease Control with target values of 0.74, 1.41, and 2.63 mmol/L, the method produced biases of +0.01, -0.05, and 0.00 mmol/L, respectively (mean: -0.01 mmol/L or -0.4%). The mean coefficient of variation was 1.4% within and 2.5% between days; the combined CV, 2.9%. Ninety 6-microL serum samples can be analyzed per hour. The method is more accurate and precise than one based on an NADH-coupled enzyme system with separate addition of lipase.

Pharmacokinetic evidence for blood flow depression in dose dependent disposition of 4-aminoantipyrine in rabbits

Pharmacokinetic relationships have been developed to characterize a one-compartment drug disposition model which includes perfusion limited elimination processes. The derived expressions have been applied to plasma concentration and urinary excretion data obtained after rapid intravenous administration of 4-aminoantipyrine to rabbits. The mathematical relationships and experimental data demonstrate that dose dependent disposition of 4-aminoantipyrine is a result of reduced renal and hepatic blood flow caused by the drug itself.

Plasma protein binding of dipyrone metabolites in man

Four metabolites of dipyrone, 4-methylaminoantipyrine (MAA), 4-aminoantipyrine (AA), 4-formylaminoantipyrine (FAA) and 4-acetylaminoantipyrine (AAA) can be identified in human plasma after its oral administration. The plasma protein binding of the metabolites in samples from 20 healthy volunteers was determined by ultrafiltration. None of the metabolites were found to be extensively bound to plasma proteins. The binding of MAA and AA was relatively higher than of FAA and AAA, as expected from their chemical structure. The mean percentage plasma protein binding was 57.6% for MAA, 47.9 for AA, 17.8 for FAA and 14.2% for AAA. The correlation between the unbound concentration in plasma and the total concentrations of MAA, AA, FAA and AAA was linear. No association was evident between the total protein plasma concentration and the extent of binding. The possible therapeutic implications related to protein binding of several analgesic and non-steroidal anti-inflammatory drugs are discussed.

Preparation and properties of primary maintenance cultures of adult rabbit hepatocytes

Static and rotary cultures of adult rabbit hepatocytes can be produced reproducibly following their isolation by means of a simplified, inexpensive recycling perfusion system. Light and electron microscopic examination of the cultures showed that these hepatocytes retained the morphological characteristics of fully differentiated hepatic parenchymal cells for up to 5 days in static culture and for up to 10 days in rotary culture, after which time they progressively degenerated and were replaced by other cell types. These hepatocytes exhibit several major metabolic functions characteristic of liver in vivo, including bromsulphthalein uptake, albumin synthesis, bilirubin conjugation, lipid synthesis, urea production and responsiveness to insulin. The xenobiotic metabolising capability of the cultured hepatocytes was much more stable than that of rat hepatocytes and the mixed function oxidase activity was typical of cytochrome P-450, rather than cytochrome P-448 as indicated by the metabolite profiles of biphenyl, aminopyrine, ethylmorphine, benzo[a]pyrene and 7-ethoxycoumarin. Treatment with phenobarbitone led to drug metabolising enzyme induction: SKF525A and alpha-naphthoflavone were effective inhibitors of drug metabolising activity.

Formation of mutagenic derivatives from nitrite and two primary amines

Sodium nitrite and two primary aromatic amines, viz. amino antipyrine (AAP) and aniline, were preincubated in vitro with human gastric juice. The resulting derivatives -- presumably diazonium salts -- were directly mutagenic in the Salmonella test. The mutagenic response was more pronounced in the case of AAP, while toxic effects narrowed the range of activity of the aniline derivative. These patterns are consistent with the findings of independent colorimetric analyses, showing that the AAP derivative is more stable at 37 degrees C than the aniline derivative.