Biomedical subjects

M Delaforge

Publications and source records attributed to M Delaforge.

At least 37 records · Page 2Linked to original sources

PubMed1997

Metabolism of 14C-labelled 5-nitro-1,2,4-triazol-3-one by rat liver microsomes--evidence for the participation of cytochrome P-450.

In the present study, we synthesized 14C-labelled 5-nitro-1,2,4-triazol-3-one (NTO) and investigated its hepatic metabolism by dexamethasone-induced murine hepatic microsomes. Under the nitrogen atmosphere, 5-amino-1,2,4-triazol-3-one was the only detected metabolite of NTO. The microsomal nitroreductase activity was dependent on NADPH, totally inhibited by carbon monoxide and partially inhibited by oxygen. In aerobic conditions, beside a low amount of amine, the major metabolite formed is the 5-hydroxy-triazolone, urazole. This compound resulted from the oxidative denitrification of NTO, which produced equivalent amount of nitrite. This reaction, like the nitroreductase activity, was dependent on NADPH and totally inhibited by carbon monoxide. Both nitroreduction and oxidative denitrification were inhibited by imidazole-related inhibitors: miconazole and methimazole, and to a less extent by N-octylamine. The microsomal denitrification was induced by the treatment of rats with dexamethasone and phenobarbital. The microsomal reductase activity is present in untreated rat microsomes, and recovered with various inducers. The results of this study indicate the role played by cytochrome P-450 in the metabolism of NTO, supported by its transformation with reconstituted cytochrome P-450 systems.

Animals↗

PubMed1997

Bromocriptine is a strong inhibitor of brain nitric oxide synthase: possible consequences for the origin of its therapeutic effects.

The ergot alkaloid bromocriptine (BKT) was found to act as a strong inhibitor of purified neuronal nitric oxide synthase (NOS) (IC50 = 10 +/- 2 microM) whereas it was poorly active towards inducible macrophage NOS (IC50 > 100 microM). BKT affects the activation of NOS by calmodulin, as it not only inhibits L-arginine oxidation to NO and L-citrulline but also NADPH oxidation and calmodulin-dependent cytochrome c reduction catalyzed by neuronal NOS. These results suggest that BKT could exert some of its therapeutic effects by interfering with the NOS-dependent formation of nitric oxide and/or superoxide ion in various tissues.

Animals↗

PubMed1997

Metabolite involvement in bromocriptine-induced prolactin inhibition in rats.

Bromocriptine (BCT) is a dopamine D2 receptor agonist used for the treatment of Parkinson's disease and hyperprolactinemic disorders. After oral administration, BCT is metabolized into mono- or dihydroxylated metabolites. To study how these metabolites influence parent drug pharmacodynamics, we administered BCT to rats intravenously (1 mg/kg i.v.) and orally (10 mg/kg p.o.) and measured the inhibition of prolactin secretion. Despite similar areas under the curve for BCT, the duration of the effect was 36 h after oral and only 18 h after intravenous administration. Pharmacokinetic/pharmacodynamic models were used to correlate the concentration of BCT in the effect compartment with the lowering of prolactin. One of these models (effect compartment model) showed that the effective concentration (EC50) at the site of action was much lower after oral (0.56 nM) than after intravenous administration (3.68 nM). In contrast, the EC50 values based on BCT metabolite data were in the same range for both administrations. These observations suggested the activity of one or more BCT metabolites. To confirm this hypothesis, hydroxylated metabolites of BCT (produced in vitro by rat liver microsomes) were administered i.v. (100 microg/kg) in rats. We found that monohydroxylated BCT was able to lower prolactin secretion like BCT. Dihydroxylated metabolites, as well as monohydroxylated metabolites, were effective in reducing in vitro prolactin secretion. Because we demonstrated that the concentration of hydroxylated metabolites after oral administration is 55-fold that of BCT, it can be concluded that BCT activity in the pituitary after oral administration is mediated by its metabolites.

Animals↗

PubMed1996

Kinetic evaluation of nitric oxide production in pleural exudate after induction of two inflammatory reactions in the rat.

NO generation in the course of two acute, non immune, inflammatory reactions (pleurisy induced by rat isologous serum and carrageenan) was assessed by means of nitrite measurement in pleural exudate from 0.5 to 24 h. NO release varied time-dependently, similarly for the two inflammatory reactions. A first, but transient, peak was reached in 30 min while a second peak, more sustained, began at the fourth hour and was maximum at the tenth. Kinetic evolution of NO release was consistent with activation, in a first step, of a constitutive NO synthase probably from endothelial origin (inhibited by 2-Methyl-2-Thiopseudourea sulfate but not by dexamethasone) and with activation, in a second wave, of inducible NOS from endothelial and exudative cells. NO release was potentiated by administration per os of L-Arginine and seems to be involved in the evolution of acute inflammatory reactions and oxygen metabolite production.

Animals↗

PubMed1996

Enzyme immunoassays for bromocriptine and its metabolites.

We have developed two bromocriptine enzyme immunoassays with different specificities for applications in human and animal pharmacokinetic studies. The first assay uses antibodies directed against the cyclopeptide structure of bromocriptine, and is specific for untransformed bromocriptine. The second assay uses antibodies directed against the bromolysergic part of the molecule and allows the measurement of both bromocriptine and its metabolites. Enzymatic tracers were obtained by covalent coupling of bromocriptine analogs to acetylcholinesterase from the electric eel Electrophorus electricus. Both assays have a limit of detection of 10 pg/ml and a limit of quantification of 50 pg/ml. The specificity of the assays was determined following fractionation by high-performance liquid chromatography of rat samples obtained after administration of bromocriptine.

Administration, Oral↗

PubMed1996

In vitro hydroxylation and epoxidation of some isomeric lauric acid analogs by rat liver microsomes. Identification of metabolites and effects of clofibrate or phenobarbital pretreatment.

The primary metabolites of a series of unsaturated lauric acid analogs (8-, 9-, 10-, and 11-dodecenoic acids) used as radiolabeled substrates for rat liver microsomes were quantitated by TLC and reverse phase-HPLC analysis, and identified by chemical derivation and GC/MS. Isomeric epoxidodecanoic acids and omega- and (omega-1)-monohydroxydodecenoic acids were essentially the only products formed from the incubations of the unsaturated fatty acids. Rat liver microsomes predominantly oxidized the terminal carbons of all substrates, leading to omega- and (omega-1)-hydroxylated metabolites, with the exception of 11-dodecenoic acid, which was efficiently converted to the epoxide. The E and Z isomers of dodecenoic acids were metabolized with the same efficiency and gave rise to the same pattern of hydroxylated vs. epoxidized products. The hydroxylation/epoxidation ratio was directly related to the position, but not to the geometry of the double bond in the aliphatic chain. Clofibrate pretreatment of the animals resulted in a strong induction of omega-oxidation, with a decrease in the ability to catalyze epoxidation of internal olefins, whereas phenobarbital pretreatment only stimulated (omega-1)-hydroxylation without any effect on epoxidation. In contrast to higher plants in which carbon 9 is the major target, rat liver cytochromes P450 selectively carried out hydroxylation (or epoxidation) at carbons 12 and 11 of lauric acid, as well as its unsaturated isomeric analogs.

Animals↗

PubMed1995

Immunostimulating lipopeptide, LtriP (RP 56142): comparison of the effect on hepatic cytochrome P 450 modulation and radioprotection in male and female of three mouse strains.

The sex-dependent effect of lauroyl-L-Ala-D-gamma-Glu-L,L-A2pmNH2 (LtriP, RP 56142) on hepatic microsomal cytochromes P 450 (cyt P 450) was studied in three mouse strains NMRI, C3H/OuJ and C3H/HeJ. In NMRI and C3H/OuJ, strains which are responsive to bacterial lipopolysaccharides (LPS-responsive), regardless of the sex of the mouse, significant decrease in the amount of cyt P 450 was observed after LtriP treatment, with a concomitant reduction in ethoxyresorufin-O-deethylase (cyt P 450 1A-dependent) and 7-ethoxycoumarin-O-deethylase activities. This was not seen in C3H/HeJ (LPS-hyporesponsive) mice. These effects may be related to LtriP-dependent cytokine induction, since neither LtriP nor LPS stimulated interleukin-1 (IL-1) secretion by C3H/HeJ macrophages. 11- and 12-hydroxylations (11- and 12-OH) of lauric acid were compared in C3H/OuJ and C3H/HeJ mice. LtriP depressed the total enzymatic conversion of lauric acid in the two strains without modification of the 11/12-OH ratio for C3H/OuJ or male C3H/HeJ mice. However, in females C3H/HeJ mice this decrease was particularly significant and concerned especially the 12-OH activity (a marker of cyt P450 4A family). Although males of the three strains were more sensitive to irradiation than females, LtriP exerted a sex-independent radioprotection on NMRI and C3H/OuJ mice. Its radioprotective effect was illustrated by the preservation of all the enzymatic activities studied in treated NMRI mice, contrary to irradiated control animals. In contrast, for the C3H/HeJ strain, males were not protected by LtriP treatment and, furthermore, females showed a marked sensitization to irradiation. The effects in CH3/HeJ strain implicate LtriP in the control of cyt P 450 induction and of sensitivity to irradiation independently of IL-1 induction.

Adjuvants, Immunologic↗

PubMed1995

Particular ability of cytochromes P450 3A to form inhibitory P450-iron-metabolite complexes upon metabolic oxidation of aminodrugs.

The ability of 21 drugs containing an amine function to form inhibitory P450-iron-metabolite complexes absorbing around 455 nm was studied on liver microsomes from rats treated with various P450 inducers. These drugs belong to different chemical and therapeutic series and exhibit very different structures. In the case of eight compounds (diltiazem, lidocaine, imipramine, SKF 525A, fluoxetine, L-alpha-acetylmethadol, methadol and desmethyltamoxifen) whose oxidation by microsomes from rats treated with several inducers was studied, only dexamethasone (DEX)-treated rat microsomes and, to a lesser extent, phenobarbital (PB)-treated rat microsomes, were able to give significant amounts of 455 nm absorbing complexes. Ten of the 21 compounds studied gave such complexes with DEX-treated rat microsomes, while only three compounds gave complexes (in low amounts) with PB-treated rat microsomes only. For all compounds leading to complexes both with DEX- and PB-treated rat microsomes, much higher amounts of complexes were obtained with DEX-treated rat microsomes. DEX-treated rat microsomes also led to the most intense type I spectral interactions with most of the compounds studied, and very often exhibited the highest N-dealkylation activities towards the tertiary or secondary amine function of the drugs used. A few exceptions aside, there generally exists a qualitative relationship between the ability of P450 3As, induced by DEX, to bind and N-dealkylate amino compounds and their propensity to lead to 455 nm absorbing complexes. This was confirmed by in vivo experiments showing that rats treated with diltiazem, tamoxifen or imipramine accumulated large amounts of 455 nm absorbing complexes in their liver only after pretreatment with DEX and, to a lesser extent, with PB. This particular ability of P450 3As to oxidize amino drugs with formation of inhibitory P450-metabolite complexes could be of great importance for the appearance of drug interactions in man.

Amines↗

PubMed1995

Conformational change due to esterification of hydroxy groups in erythromycin A and its major metabolite: analysis of these derivatives with different biological properties using NMR and molecular dynamics (MD) data.

A conformational study is performed on the acylated erythromycin and erythralosamine derivatives from comparison between experimental results (NMR) and theoretical calculations by Molecular Dynamics (MD) in attempts to correlate their conformations with their abilities to generate cytochrome P450-nitroso metabolite complexes in vitro. As the 3'-dimethyl-amino function of the desosamine is metabolized and responsible for the interaction with cytochrome P450, its position, mobility and steric hindrance in the proximity of this functional group are related to its biological properties. The major conformations of the lactone ring were termed A (A1, A2, A3) and B (B1, B2), and this macrocycle flexibility induced five different orientations a, b, c, d and e for the desosamine sugar. Conformations A and B differ in many ways but the major change is the inward folding of the C(3) fragment in B. Conformer a exhibits an orientation of the desosamine nearly perpendicular to the macrocycle whereas the two units are in the same plane in conformations c and e. For conformation b, the cladinose unit lifts up above the macrocycle. Conformation d exhibits a turned-back cladinose. In the erythromycin derivatives esterification at the beta position to the N(CH3)2 group of the desosamine reduces the degree of freedom of the macrocyclic lactone ring which corresponds to conformation A only. The desosamine sugar was found to be perpendicular to the macrocycle (a conformer) and both sugar groups are parallel to reduce the steric energy. In the erythralosamine derivatives, the macrocycle is always present as conformation B with the two conformations b and c of the sugar rings. The steric parameters favour the b conformers in which the amino group is tilted up, while in 3,2'-dibenzoylated stacking aromatic attraction stabilizes the planar c conformer. Both isomers are thus shown to adopt well-defined conformations and to be well-adapted for a comparative structure-activity correlation studies. There is a significant relationship between the conformation b and the formation of cytochrome P450-nitroso metabolite complexes.

Acylation↗

PubMed1995

Nitric oxide formation during the cytochrome P-450-dependent reductive metabolism of 18-nitro-oxyandrostenedione.

18-Nitro-oxyandrostenedione (18-ONO2A), a potential mechanism-based inhibitor of the last steps of aldosterone biosynthesis, is well recognized by different cytochrome P-450s, which are able to metabolize it reductively into nitric oxide (NO) and 18-hydroxyandrostenedione. Rat liver microsomal P-450s are able to carry out this reaction with increased efficiency under anaerobic conditions. P-450 3A isozymes induced upon treatment of rats with dexamethasone or troleandomycin were best able to bind and metabolize 18-ONO2A. This reaction was shown to occur in the presence of dioxygen as well, suggesting that it may be of physiological relevance. The formation of NO was detected as a transient P-450-Fe(II)NO complex by UV-visible and EPR spectroscopy. In addition, steroidogenic tissues containing cytochrome P-450s such as bovine adrenal mitochondria or human placental microsomes also were capable of binding and metabolizing 18-ONO2A as judged by the formation of an Fe(II)NO complex. This recognition of a steroid nitrate, a potential antialdosterone and its subsequent metabolism under reductive conditions to generate NO both in hepatic and steroidogenic tissues, can be of pharmacological interest, because NO has been demonstrated to modulate steroidogenesis in addition to other processes such as vascular relaxation, neurotransmission or cytostasis. A nitrate derivative of a steroid could perhaps act as a vectorized NO precursor in which the steroid moiety is targeted specifically to steroid receptors or steroidogenic tissues, thus leading to localized NO liberation.

Adrenal Glands↗

PubMed1994

Reactions of prostaglandin H synthase with monosubstituted hydrazines and diazenes. Formation of iron(II)-diazene and iron(III)-sigma-alkyl or iron(III)-sigma-aryl complexes.

The reaction of p-chlorophenylhydrazine with prostaglandin H synthase (PGHS) Fe(III) under aerobic conditions leads to a partial destruction of the heme and to a new complex absorbing at 436 nm. This complex is also obtained by reaction of p-chlorophenyldiazene (pClPhN = NH) with PGHS Fe(III) under anaerobic conditions and by oxidation of the PGHS Fe(II)(pClPhN = NH) diazene complex by Fe(CN)6K3. The similarity between those reactions and those of arylhydrazines and aryldiazenes with other hemoproteins such as cytochrome P450 and hemoglobin and myoglobin, as well as the similarities between the spectroscopic and chemical properties of this complex and those of the sigma-aryl complexes of other hemoproteins such as hemoglobin and myoglobin, strongly suggested a PGHS Fe(III)-pClPh structure for this complex. It was completely established after the extraction of its heme, by butan-2-one at 0 degree C under neutral or acidic conditions, which led to the sigma-aryl PGHS-Fe(III)-pClPh complex and to N-phenylprotoporphyrin IX, respectively. A mechanism is proposed for the formation of the PGHS Fe(III) pClPh complex; it includes the reduction of PGHS Fe(III) into PGHS Fe(II) with formation of the diazene pClPhN = NH. This diazene can bind to PGHS Fe(II) or be oxidized with formation of pClPh free radicals. These radicals can react with PGHS Fe(II) to form the PGHS Fe(III)-pClPh complex or with the protein, or may initiate free radical oxidations which could lead to destruction of the heme or of the protein. Other alkylhydrazines or arylhydrazines also react with PGHS Fe(III) under aerobic conditions with the formation of PGHS Fe(III)-R or aryl (Ar) complexes and heme destruction. Alkylhydrazines such as methylhydrazine, which lead to very reactive alkyl radicals, lead to very low amounts of PGHS Fe(III)-R complex and high amounts of heme destruction, whereas arylhydrazines bearing electron-withdrawing substituents such as 3,4-dichlorophenylhydrazine, which lead to stabilized aryl radicals, lead to a high amounts of PGHS Fe(III)-Ar complex and low amounts of heme destruction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

N omega-hydroxyl-L-arginine, an intermediate in the L-arginine to nitric oxide pathway, is a strong inhibitor of liver and macrophage arginase.

N omega-Hydroxy-L-arginine (L-NOHA) is a potent inhibitor of the hydrolysis of L-arginine (L-Arg) to L-ornithine (L-Orn) catalyzed by purified bovine liver arginase (BLA). It appears as one of the most powerful arginase inhibitors reported so far (Ki = 150 microM). The other products of NO synthase are either without effect (NO2-, NO3-) or much weaker inhibitors (L-citrulline (L-Cit) and NO) of BLA. Products derived from a possible hydrolysis of L-Arg (L-Orn and urea) or of L-NOHA (L-Cit, hydroxyurea and hydroxylamine) are also inactive toward BLA at concentrations up to 2 mM. The configuration of L-NOHA is important as D-NOHA is much less active, and its free -COOH and alpha-NH2 functions are required for recognition of BLA. L-NOHA is also a potent inhibitor of the arginase activity of rat liver homogenates and of murine macrophages (IC50 of 150 and 450 microM, respectively). These remarkable properties of L-NOHA could play a role in the modulation of the biosynthesis of the biological mediator NO by increasing local L-Arg concentrations.

Animals↗

PubMed1994

High affinity of ergopeptides for cytochromes P450 3A. Importance of their peptide moiety for P450 recognition and hydroxylation of bromocriptine.

The interaction between rat and human liver cytochromes P450 with a series of lysergic acid derivatives and ergopeptide alkaloids was studied by difference visible spectroscopy. Ergopeptides, like bromocriptine, ergocryptine and dihydroergotamine, strongly interacted with rat liver microsomes with the appearance of a difference spectrum which is characteristic of their binding to a protein site close to the heme. The intensity of this spectrum was clearly dependent on the amounts of P450s 3A in the microsomes and was at its maximum in dexamethasone-treated rat microsomes. All the ergopeptides studied exhibited a high affinity for rat P450s 3A (Ks around 1 microM), although lysergic acid derivatives not bearing the tripeptide moiety failed to give significant interactions with these P450s. A cyclic azatripeptide exhibiting a structure very similar to that of the tripeptide moiety of ergopeptides also interacted with P450s 3A with appearance of an intense type I difference spectrum. Very similar results were observed with two allelic forms of human liver P450 3A4, P450 NF25 and P450 hPCN1, produced in yeast. In both cases all the ergopeptides studied showed high affinities for the P450s (Ks 0.6-2.2 microM) and an intense shift from the low-spin to the high-spin state upon substrate binding (60-100% spin shift). Lysergic acid derivatives not bearing the tripeptide group of ergopeptides also completely failed to interact with P450s 3A4. Liver microsomes from rats pretreated with dexamethasone, a specific inducer of P450 3A, were found to be particularly active for the hydroxylation of bromocriptine, which occurs at the level of its tripeptide moiety. Human liver microsomes as well as P450 NF25 and P450 hPCN1 also exhibited a high activity for bromocriptine hydroxylation at this level. These results show that ergopeptides exhibit a particularly high affinity for P450s of the 3A subfamily. The tripeptide moiety of ergopeptides is essential for their recognition by P450s 3A and binds at a site close to P450 heme, producing type-I difference spectra. Accordingly, at least one of the studied ergopeptides, bromocriptine, is hydroxylated by P450s 3A at the proline ring of the cyclopeptide moiety. As cyclosporine is known to be a good substrate of P450s 3A, these results suggest that P450s 3A may be especially prone in a general manner to recognize and oxidize peptides or pseudopeptides.

Animals↗

PubMed1994

Dehydration of alkyl- and arylaldoximes as a new cytochrome P450-catalyzed reaction: mechanism and stereochemical characteristics.

The Z isomers of benzaldoxime and 4-(hexyloxy)benzaldoxime were dehydrated into the corresponding nitriles in the presence of rat liver microsomes and NADPH or dithionite. Their E isomers remained unchanged under identical conditions. Alkylaldoximes, like phenylacetaldoxime and heptanaldoxime, are also dehydrated under these conditions, the alkylaldoximes being more rapidly transformed than the arylaldoximes. A genetically well-defined P450 expressed in yeast, P450 3A4, the major P450 isozyme in human liver, was also found to be catalytically active for dehydration of (Z)-benzaldoxime. All these reactions were found to be catalyzed by P450 Fe(II) as they required the use of intact microsomes in the presence of NADPH or dithionite and were strongly inhibited by O2 and CO as well as by classical P450 inhibitors. A P450 complex characterized by a Soret peak at 442 nm was detected during these reactions; its disappearance was found to be concomitant with the consumption of the aldoxime and the formation of the corresponding nitrile. (E)-benzaldoximes and all the studied ketoximes failed to give such complexes with P450 Fe(II). On the basis of these results, a possible mechanism for this new P450 reaction is proposed. It involves a P450 Fe(II)<--N(OH)=CHR complex as a key intermediate and a charge transfer from P450 Fe(II) to the aldoxime C=N bond which results in a cleavage of the aldoxime N-O bond.

Animals↗

PubMed1993

Particular ability of liver P450s3A to catalyze the oxidation of N omega-hydroxyarginine to citrulline and nitrogen oxides and occurrence in no synthases of a sequence very similar to the heme-binding sequence in P450s.

Liver microsomes from rats pretreated with various inducers of P450 isoforms exhibit very different abilities to catalyze the oxidation of N omega-hydroxy-L-arginine (NOHA) by NADPH and O2 with formation of citrulline and nitrogen oxides. Treatment of rats with dexamethasone, a classical inducer of P450 3A, leads to a spectacular 7-fold increase of the activity found for untreated rats, while induction by phenobarbital causes a much lower increase of this activity and induction by 3-methylcholanthrene or clofibrate decreases it. Specific inhibitors of P450s3A as troleandomycin and dihydroergotamine strongly inhibit NOHA oxidation whereas metyrapone, an inhibitor of other P450 subfamilies, was without effect. These data show the particular ability of P450s of the 3A subfamily to catalyze the second step of the oxidation of L-arginine by NO synthases (NOS). This analogy between NOSs and P450s3A is further substantiated by a protein sequence comparison which shows that a 9-amino acid segment present in all NOSs exhibits a strong similarity with the sequence mainly responsible for heme binding in P450s3A which is well conserved in all P450s. This segment contains all the structural factors which are thought to be crucial for heme binding in P450s.

Amino Acid Oxidoreductases↗

PubMed1993

Particular ability of cytochrome P-450 CYP3A to reduce glyceryl trinitrate in rat liver microsomes: subsequent formation of nitric oxide.

Glyceryl trinitrate was denitrated in rat hepatic subcellular fractions, with formation of glyceryl dinitrates and glyceryl mononitrates. Among differently treated-rat liver microsomes, the highest microsomal activity was obtained under anaerobic conditions with microsomal preparations from dexamethasone-treated rats and NADPH. The reaction was inhibited by O2, CO, miconazole, dihydroergotamine and troleandomycin showing that it was catalyzed by cytochrome P-450 CYP3A isoforms. The formation of a transient cytochrome P-450 Fe(II)-NO complex during this reaction was shown by visible spectroscopy. The cytosolic activity was shown to be dependent on glutathione and glutathione transferase and was not inhibited by dioxygen. In the hepatic 9000 x g supernatant containing both NADPH and cytochrome P-450 and glutathione and glutathione transferase, the cytochrome P-450-dependent reaction accounts for 30-40% of the total denitration activity observed under anaerobic conditions, using 100 microM GTN.

Animals↗

PubMed1993

Lack of effect of phenobarbital on ex vivo leukocyte oxidative metabolism in healthy volunteers.

Oxidative metabolism in activated human polymorphonuclears catabolizes leukotriene B4 by a cytochrome P450 omega-hydroxylase and procainamide by a myeloperoxidase. The percentage of leukotriene B4 metabolized by activated human polymorphonuclears and the apparent enzymatic parameters of procainamide metabolism were studied ex vivo in six healthy volunteers before and after phenobarbital intake (100 mg/day) for 10 days and in six healthy control volunteers. No differences were found between groups for the difference in percentage of leukotriene B4 metabolized between day 11 and day 1. The apparent enzymatic parameters, Km and Vm, of procainamide oxidation did not differ significantly between the groups both on day 1 and day 11. These results do not show any evidence of inducibility of leukotriene B4 and procainamide metabolism in human polymorphonuclears. However, a positive correlation between 6 beta OH-cortisol excretion and percentage of leukotriene B4 metabolized was observed on day 11. This study suggests that human polymorphonuclears cytochrome P450 leukotriene B4 omega-hydroxylase and procainamide metabolism is not a useful method to study cytochrome P450 induction in clinical pharmacology.

17-Hydroxycorticosteroids↗

PubMed1992

Cytochrome P450 catalyzes the oxidation of N omega-hydroxy-L-arginine by NADPH and O2 to nitric oxide and citrulline.

Rat liver microsomes catalyze the oxidative denitration of N omega-hydroxy-L-arginine (NOHA) by NADPH and O2 with formation of citrulline and nitrogen oxides like NO and NO2-. Besides NO2- and citrulline, whose simultaneous formation is linear for at least 20 min, the formation of NO could be detected under the form of its P450 and P420-Fe(II) complexes by UV-visible and EPR spectroscopy. Classical inhibitors of NO-synthases, like N omega-methyl-and N omega-nitro-arginine, fail to inhibit the microsomal oxidation of NOHA to citrulline and NO2-. On the contrary classical inhibitors of hepatic cytochromes P450 like CO, miconazole, dihydroergotamine and troleandomycin, strongly inhibit this monooxygenase reaction. These results show that the oxygenation of NOHA by NADPH and O2 with formation of citrulline and NO can be efficiently catalyzed by cytochromes P450 (with rates up to 1.5 turnovers per min for the cytochromes of the 3A subfamily).

Animals↗