Metabolizers Of Sparteine Research Articles

Codeine increases pain thresholds to copper vapor laser stimuli in extensive but not poor metabolizers of sparteine

The analgesic efficacy and kinetics of a single oral dose of 75 mg codeine was investigated in 12 extensive metabolizers and 12 poor metabolizers of sparteine in a double-blind, placebo-controlled crossover study. The cosegregation of the O-demethylation of codeine to morphine with the sparteine oxidation polymorphism was confirmed. Hence morphine could not be detected in the plasma of any of the poor metabolizers, whereas detectable morphine plasma levels were found in 10 of 12 extensive metabolizers. Pain thresholds to laser stimuli were determined before drug intake and 90, 150, and 210 minutes after drug intake. Codeine significantly increased the pricking pain thresholds in the extensive metabolizers (p less than 0.05), whereas there were no significant changes in the poor metabolizers. No change in pain thresholds occurred with placebo in any of the two phenotypes. In the extensive metabolizers there was a significant positive correlation between the increase in pain threshold and plasma concentration of codeine. The study supports the hypothesis that morphine formation is essential for achievement of analgesia during codeine treatment.

Nonlinear Kinetics of Imipramine in Low and Medium Plasma Level Ranges

Steady state plasma concentrations of imipramine and desipramine were studied at three to nine different imipramine dose levels in 17 extensive metabolizers of sparteine and at two dose levels in two poor metabolizers of sparteine, all treated for diabetic neuropathy symptoms. The imipramine doses were changed stepwise from doses yielding plasma concentrations of imipramine plus desipramine below 150 nM, up to doses yielding therapeutic drug levels of at least 300-500 nM. The imipramine doses required to achieve therapeutic drug levels was 20 or 25 mg/day in the two poor metabolizers and 50-350 mg/day in the extensive metabolizers. In the extensive metabolizers, the concentration/dose ratio increased for imipramine and desipramine with increasing dose. Dose adjustments based on a simple linear prediction from drug levels at initial dose (50 or 75 mg imipramine/day) thus would result in 0-130% (median, 20%) overestimates, most pronounced in patients with initial low steady state levels. The nonlinear kinetics of imipramine thus may be a significant clinical problem in patients treated for diabetic neuropathy symptoms.

Sparteine Metabolism Capacity in Human Liver: Structural Variants of Human P450IID6 as Assessed by Immunochemistry

An antibody raised against rat P450dbl was used to examine the heterogeneity of the human enzyme involved in the sparteine/debrisoquine polymorphism. The extent to which the antibody was able to inhibit sparteine metabolism varied in different human livers (10-80%, n = 9) and reflected the amount of sparteine metabolism carried out by the polymorphic P450IID6 in individual liver specimens. The individual sample variation in inhibition by the antibody correlated with the inhibition caused by quinidine, a prototype competitive inhibitor of the P450IID6 enzyme active site. Western immunoblots of the liver microsomes confirmed that the variation in the inhibition of sparteine metabolism by this antibody reflected the amount of P450IID6 protein. In addition, a detailed study of one of the livers (K19) which demonstrated a lack of inhibition by the antibody was performed which confirmed the lack of P450IID6 in this liver specimen and suggested that the nascent sparteine metabolism activity was due to other forms of P450.

The use of stable isotope label — high resolution NMR technique for metabolic studies the metabolism of sparteine

The use of stable isotope label — high resolution NMR technique for metabolic studies the metabolism of sparteine

A dose‐effect study of the in vivo inhibitory effect of quinidine on sparteine oxidation in man.

1. Twelve healthy extensive metabolisers of sparteine were sparteine tested daily for 6 days (19.00 h to 07.00 h). A small but statistically significant rise in sparteine metabolic ratio (MR) was observed. 2. Following 100 mg quinidine sulphate given to four of the subjects at 16.00 h, sparteine tests were carried out 19.00 h to 07.00 h on the same day and then daily for 6 days. Quinidine caused an immediate twenty-fold increase in sparteine-MR which then gradually returned to normal over the following 4-6 days. Quinidine concentrations in plasma were measurable only up to 20 h after the quinidine test dose. 3. At weekly intervals, all 12 subjects received single doses of quinidine sulphate of 5, 10, 20, 40 and 80 mg at 16.00 h, each time followed by a sparteine test 19.00 h to 07.00 h on the same day. A clear dose-effect relationship was found with a significant rise in the sparteine-MR even after 5 mg quinidine. After 80 mg quinidine, 8 of 12 subjects became phenotypically poor metabolisers (MR greater than 20).

Quinidine kinetics after a single oral dose in relation to the sparteine oxidation polymorphism in man.

The kinetics at a single oral dose (400 mg) of quinidine were studied in four extensive metabolizers (EM) and four poor metabolizers (PM) of sparteine. The clearance of quinidine by 3-hydroxylation was significantly lower in PM than in EM, but the difference was small (25-30%). This finding suggests that 3-hydroxylation, in part, is catalyzed by the same isoenzyme of cytochrome P450, P450db1 which oxidizes sparteine. Otherwise, no significant phenotypic differences in total or metabolic clearance were found and it is concluded that the metabolism of quinidine is largely carried out by P450 isoenzymes different from P450db1. A biexponential decline in the log plasma quinidine concentration vs time curves was observed in all subjects, and the mean elimination half-life was 11-12 h. This is about twice as long as generally reported in the literature.

Kinetics ofin vitrometabolism of methoxyphenamine in rats

1. Methoxyphenamine (MP) was metabolized in vitro by rat liver preparations to O-desmethylmethoxyphenamine (O-desmethyl-MP), N-desmethylmethoxyphenamine (N-desmethyl-MP) and 5-hydroxymethoxyphenamine (5-hydroxy-MP). These metabolic pathways were inhibited by SKF 525-A and carbon monoxide, which indicates that these reactions were mediated at least partly by an NADPH-dependent cytochrome P-450 system. 2. Strain differences in the metabolism of this drug in vitro were observed in female Lewis and Dark Agouti (DA) rats, which are proposed models for human debrisoquine phenotypes. Methoxyphenamine O-demethylase and 5-hydroxylase activity in DA rats were lower than those in Lewis rats. 3. The metabolic transformation of methoxyphenamine in vitro to O-desmethyl-MP was inhibited competitively by debrisoquine and sparteine. This indicates that the cytochrome P-450 isoenzyme mediating the metabolism of MP to O-desmethyl-MP is similar to that mediating metabolism of debrisoquine and sparteine. However, no inhibition was observed with methenytoin.

Polymorphic sparteine metabolism and amyotrophic lateral sclerosis.

The activity of detoxication with the cytochrome P450 family of enzymes was studied in patients with amyotrophic lateral sclerosis (ALS). The metabolic ratio (MR) of sparteine sulphate was measured, and the population of phenotypes for sparteine nitro (N)-oxidation was determined in 30 patients with ALS and 41 controls for the assay of the sparteine N-oxidation by the cytochrome P450 enzymes. A lower MR and higher frequency of efficient metabolizers were observed in the ALS group, suggesting that there is efficient sparteine N-oxidation by cytochrome P450 pathways in ALS. This tendency was more marked in 15 patients with ALS aged under 60 years.

Debrisoquine oxidation phenotype in psychiatric patients.

Between 5% and 10% of Caucasian populations exhibit poor metabolism of debrisoquine and sparteine (Clark 1985). Results obtained by our group indicate that among the Spanish population the percentage of poor metabolizers of debrisoquine is around 6% (Benítez et al. 1988). Generally the poor-metabolizer phenotype is at increased risk of toxicity when treated with drugs subjected to oxidative metabolism by the debrisoquine/sparteine type of path-way (Idle et al. 1983). A significant correlation between nortriptyline clearance and debrisoquine metabolic ratio has been demonstrated by Bertilsson et al. (1980). Steady-state concentrations of desipramine have also been shown to be highly correlated with the debrisoquine metabolic ratio (Bertilsson and Aberg-Wistedt 1983; Spina 1987).KeywordsPsychiatric PatientPoor MetabolizersExtensive MetabolizersMetabolic RatioNeuroleptic DrugThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Quinidine inhibits the 2-hydroxylation of imipramine and desipramine but not the demethylation of imipramine.

On separate occasions 6 extensive metabolizers of sparteine took a single oral dose of 100 mg imipramine and desipramine before and during the intake of quinidine sulphate 200 mg/day. During quinidine the total oral clearance of imipramine on average was reduced by 35%, and that of desipramine by 85%. The clearance of imipramine via demethylation was not significantly reduced during quinidine administration, whereas its clearance by other pathways, largely 2-hydroxylation, was reduced by more than 50%. 2-OH-Imipramine and 2-OH-desipramine were detected in plasma before (maximum concentrations 30-100 nmol.l-1) but not during quinidine. It appears that quinidine is a potent inhibitor of the sparteine/debrisoquine oxygenase, P450dbl, which is responsible for the 2-hydroxylation of imipramine and desipramine, but not of the P450 isozyme responsible for the demethylation of imipramine.

Xenobiotic and endobiotic inhibitors of cytochrome p-450dbl function, the target of the debrisoouine/sparteine type polymorphism

Five to 10% of Caucasians are poor metabolizers (PM) of debrisoquine, sparteine, bufuralol and numerous other drugs. A deficiency in cytochrome P-450dbl (P-450dbl) function is the cause of this polymorphism of drug oxidation with autosomal recessive inheritance. In the present study, inhibition of bufuralol-1'-hydroxylase in human liver microsomes by drugs and chemicals was performed in a search for potential new substrates for this polymorphic enzyme. Among the 80 alkaloids and drugs tested, 25 were competitive inhibitors. In vitro competitive inhibition of bufuralol oxidation by a substance indicates that this compound is able to bind to the same enzymatic site as bufuralol. This may mean that the competing drug also is metabolized by P-450dbl and that its metabolism is subject to the same genetic variation as the oxidation of bufuralol. However, some of these competitive inhibitors are not oxidized by P-450dbl. In this case, however, they may interfere with the in vivo phenotyping procedure by inhibiting the formation of metabolites of test drugs such as debrisoquine, sparteine, metoprolol or dextrometorphan.

Absence of hepatic cytochrome P450bufI causes genetically deficient debrisoquine oxidation in man.

The common genetic deficiency of drug oxidation known as debrisoquine/sparteine-type polymorphism was investigated with bufuralol as prototype substrate. In human liver microsomes the 1'-hydroxylation of bufuralol is catalyzed by two functionally distinct P-450 isozymes, the high-affinity/highly stereoselective P450bufI and the low-affinity/nonstereoselective P450bufII. We demonstrate that P450bufI is unique in hydroxylating bufuralol in a cumene hydroperoxide (CuOOH) mediated reaction whereas P450bufII is active only in the classical NADPH- and O2-supported monooxygenation. In microsomes of liver biopsies of in vivo phenotyped poor metabolizers of debrisoquine or sparteine, the CuOOH-mediated activity was drastically reduced. Rabbit antibodies against a rat P-450 isozyme with high bufuralol 1'-hydroxylase activity (P450db1) precipitated exclusively P450bufI-type activity from solubilized microsomes. Western blotting of microsomes with these antibodies revealed a close correlation between the immunoreactive protein and CuOOH-mediated (+)-bufuralol 1'-hydroxylation. No immunoreactive protein was detected in liver microsomes of in vivo phenotyped poor metabolizers. These data provide evidence for a specific deficiency of P450bufI and are consistent with the complete or almost complete absence of this protein in the liver of poor metabolizers.

First-pass metabolism of imipramine and desipramine: impact of the sparteine oxidation phenotype.

Four rapid extensive metabolizers (EM), four slow EM, and three poor metabolizers (PM) of sparteine were given single intravenous doses of 50 mg imipramine and desipramine. All subjects had previously taken single oral doses (100 mg) of imipramine and desipramine. The first-pass metabolism of imipramine and desipramine ranged from 23% to 73% and 0% to 48%, respectively, and was more pronounced for both drugs in EM than in poor metabolizers. The study suggested saturable 2-hydroxylation of imipramine and desipramine during the first-pass through the liver, especially in EM.

The oxidative metabolism of sparteine in the Cuna Amerindians of Panama: absence of evidence for deficient metabolizers.

Sparteine sulfate (50 mg) was administered to 170 Cuna Amerindians, 142 of whom were unrelated, and the drug and its dehydrometabolites were determined in the 0- to 12-hour urine samples. The log10 of the metabolic ratio was unimodally, but not normally, distributed and showed the following values: mean -0.21 +/- 0.26, median -0.24, limits -0.73 and 0.76, skewness 1.00, and kurtosis 4.95. On the basis of these results, it can be concluded that there are no deficient metabolizers in the Cuna sample population studied. However, the similarity of the skewness found between the Cuna sample population studied and the extensive Canadian white group, as well as an inflection point at 6.3 U in the former's probit plot, suggests the existence of at least two subgroups congregating within the same single mode in the frequency distribution curve. The use of the inflection point is discussed thoroughly, concluding that although it does not allow exclusion of the existence of genotypically different subgroups, the limitations of the data do not permit its use to determine the number of heterozygotes and thus the existence of polymorphism. The possibility of an isozyme variant, consistent with the general genetic structure of Amerindians, as suggested by the coexistence of two subgroups within the unimodal curve, is entertained.

Apparent Mendelian recessive inheritance of sparteine metabolism in an extended Japanese family

Apparent Mendelian recessive inheritance of sparteine metabolism in an extended Japanese family

Evidence for polymorphic oxidation of sparteine in Japanese subjects.

The metabolism of sparteine which exhibits a genetic polymorphism in Caucasians was studied in 84 unrelated Japanese subjects. In contrast to a recent study where debrisoquine was used as a probe and no poor metabolizers could be observed in Japanese involving 100 subjects, two subjects had a urinary metabolic ratio of sparteine greater than 20 and thus were poor metabolizers of sparteine. The incidence of poor metabolizer phenotype of sparteine oxidation of 2% seems to be lower in Japanese as compared with various Caucasian populations where 5 to 10% are poor metabolizers of sparteine. However, this is not conclusive, because the 95% confidence interval of the observed frequency, 0.6 to 8%, covers the range reported in the literature for Caucasians.

Evidence for altered catalytic properties of the cytochrome P-450 involved in sparteine oxidation in poor metabolizers.

Sparteine metabolism was studied in human liver microsomes from nine extensive ([EM] urinary metabolic ratio [MR] less than 20) and four poor metabolizers ([PM] MR greater than 20). The formation of 2- and 5-dehydrospartein displayed monophasic Michaelis-Menten kinetics. In livers from PMs the formation of the major sparteine metabolite 2-dehydrosparteine was characterized by more than a thirtyfold increase in Michaelis-Menten constant (Km)(1880 +/- 1044 mumol/L) as compared with EM subjects with an MR less than 1 (58.3 +/- 38.8 mumol/L). EM subjects with an MR greater than 3 who may constitute heterozygous metabolizers showed Km values in between (658 +/- 301 mumol/L). There was no difference in maximum rate of metabolism (Vmax) of 2-dehydrosparteine formation between EM and PM subjects (101 +/- 39 vs. 86 +/- 52 pmol/min/mg). The formation of 5-dehydrosparteine exhibited a Km of 100 +/- 123 mumol/L similar to the Km of 2-dehydrosparteine formation. The urinary MR correlated positively with the Km for 2-dehydrosparteine formation. The intrinsic clearance for 2-dehydrosparteine showed a highly significant negative correlation with the MR. The pronounced differences in Km together with the significant correlation between Km and MR with no marked differences in Vmax between phenotypes suggest that the impaired oxidation capacity in PM subjects is more likely the result of a P-450 isozyme with altered catalytic properties rather than a decreased amount of enzyme.

Methoxyphenamine O-demethylase and 5-hydroxylase: A GLC-ECD assay to study their activities and their inhibition by debrisoquine and sparteine

A GLC-ECD method is described for the determination of the O-desmethyl, N-desmethyl and aromatic 5-hydroxy metabolites of methoxyphenamine in liver homogenates. The O-desmethyl and 5-hydroxy metabolites are deficient in poor metabolizers of debrisoquine and sparteine and the Dark Agouti rat model of this human phenotype. The present analytical method can be useful in determining methoxyphenamine O-demethylase and 5-hydroxylase activities as well as identifying those substrates which inhibit these and are worthy of further study.

Sparteine oxidation polymorphism: a family study.

Polymorphic oxidation of the pharmacogenetic probe drug sparteine was investigated in 35 parents and 29 siblings of 20 unrelated poor metabolizer (PM) probands. Phenotyping was carried out on the basis of metabolic ratio (MR) = sparteine/dehydrosparteines in the 12 h urine. The distribution of MR was bimodal: 47 relatives (20 siblings and 27 parents) had MR ranging from 0.22-12 and were defined as extensive metabolizers (EM) whereas MR ranged from 20-340 in nine siblings and eight parents thus defined as PM. The 20 pedigrees confirmed that poor metabolism of sparteine is inherited as an autosomal recessive character. The mean recovery of dehydrosparteines (% of dose) was 27% in 23 positively identified drug free heterozygotes compared with 37% in unrelated EM (both genotypes) (P less than 0.05) previously phenotyped. Degrees of dominance of 73% and 77% were calculated on basis of log excretion of dehydrosparteines (% of dose in 12 h urine) and log MR, respectively.

The genetic polymorphism of sparteine metabolism.

The formation of the two major metabolites of the antiarrhythmic and oxytocic drug sparteine (2- and 5-dehydrosparteine) exhibits a genetic polymorphism. Two phenotypes, extensive (EM) and poor metabolizers (PM) are observed in the population. The frequency of the PM phenotype in various populations (Caucasian and Japanese) ranges from 2.3 to 9%. The metabolism of sparteine is determined by two allelic genes at a single gene locus. PM subjects are homozygous for an autosomal recessive gene. The metabolism of sparteine is predominantly under genetic control as treatment with drugs such as antipyrine and rifampicin known to induce oxidative drug metabolism elicited only marginal changes in sparteine metabolism. The formation of 2-dehydrosparteine in human liver microsomes from EM and PM subjects showed a more than 40-fold difference in Km between EM and PM subjects. However, Vmax-values were almost identical in both groups. These data indicate that the basis of the differences in oxidative capacity between EM and PM subjects is more likely to be due to a variant isozyme with defective catalytic properties than to a decreased amount of the isozyme.