Does hepatic metabolism of melatonin affect the endogenous serum melatonin level in man?

Melatonin (MT) is metabolized in the liver by cytochrome P450 (CYP) 1A2 but its importance for the metabolic process has not been fully elucidated. Therefore, the objective of this investigation was to study whether patients with different CYP1A2 activity would have different nocturnal serum MT levels. For that purpose serum MT concentrations were determined every second hour during the night in 12 healthy subjects and their MT areas under the curve (MT-AUCs) were calculated. Caffeine (CA) clearance was determined in advance. It is generally accepted that CA clearance reflects CYP1A2 activity. This made it possible to evaluate whether a relationship prevails between endogenous MT-AUCs and CYP1A2 activity. If CYP1A2 is of importance for the metabolism of MT one would expect to find an inverse correlation between the MT-AUCs and the CA clearance. However, such correlation did not exist in the current study (Rs=-0.021, NS). Since endogenous MT-AUC is dependent not only on MT elimination by CYP1A2 but also on MT secretion, it is possible that an increased MT secretion counter-balances an increased hepatic MT metabolism. If so, this could explain why the MT-AUCs and the CA clearance values were not inversely correlated in this study.

Orally given melatonin may serve as a probe drug for cytochrome P450 1A2 activity in vivo: a pilot study.

BACKGROUND: Melatonin is a hormone that is metabolized by cytochrome P450 (CYP) 1A2 to its main primary metabolite 6-hydroxymelatonin. We therefore evaluated the utility of oral melatonin as a marker of hepatic CYP1A2 activity. METHODS: Twenty-five milligrams of melatonin was given at 9:30 am to 12 healthy Swedish volunteers, who had previously been phenotyped for CYP1A2 with caffeine. Melatonin and conjugated 6-hydroxymelatonin were analyzed by liquid chromatography-mass spectrometry in blood samples taken between 0.5 and 6.5 hours after drug intake. Serum concentrations of melatonin and conjugated 6-hydroxymelatonin, or their ratio at different time points, and the apparent melatonin clearance were tested for correlation with caffeine clearance. RESULTS: We found a significant correlation between apparent clearance of melatonin and caffeine clearance with a Spearman rank correlation coefficient (Rs) of 0.75 (P =.005). The melatonin concentration 1.5 hours after administration also closely correlated with the caffeine clearance (Rs = -0.62; P =.03). Inclusion of conjugated 6-hydroxymelatonin gave no closer correlations. CONCLUSION: Melatonin might be developed as an alternative to caffeine as a probe drug for CYP1A2 phenotyping.

Cytochrome P450 isoforms involved in melatonin metabolism in human liver microsomes.

OBJECTIVE: The present study was carried out to identify the cytochrome P450 enzyme(s) involved in the 6-hydroxylation and O-demethylation of melatonin. METHODS: The formation kinetics of 6-hydroxymelatonin and N-acetylserotonin were determined using human liver microsomes and cDNA yeast-expressed human enzymes (CYP1A2, 2C9 and 2C19) over the substrate concentration range 1-1000 microM. Selective inhibitors and substrates of various cytochrome P450 enzymes were also employed. RESULTS: Fluvoxamine was a potent inhibitor of 6-hydroxymelatonin formation, giving 50 +/- 5% and 69 +/- 9% inhibition at concentrations of 1 microM and 10 microM, respectively, after incubation with 50 microM melatonin. Furafylline, sulphaphenazole and omeprazole used at low and high concentrations substantially inhibited both metabolic pathways. cDNA yeast-expressed CYP1A2, CYP2C9 and CYP2C19 catalysed the formation of the two metabolites, confirming the data obtained with specific inhibitors and substrates. CONCLUSIONS: Our results strongly suggest that 6-hydroxylation, the main metabolic pathway of melatonin, is mediated mainly, but not exclusively, by CYP1A2, the high-affinity enzyme involved in melatonin metabolism, confirming the observation that a single oral dose of fluvoxamine increases nocturnal serum melatonin levels in healthy subjects. Furthermore, the results indicate that there is a potential for interaction with drugs metabolised by CYP1A2 both at physiological levels and after oral administration of melatonin, while CYP2C19 and CYP2C9 are assumed to be less important.

[Adverse effects of drugs in patients with heart disease lead to hospital care]. / Läkemedelsbiverkningar leder till sjukhusvård för hjärtpatienter.

Polypharmacy in patients with cardiovascular disease leads to an increased risk of developing adverse effects. At the Department of Internal Medicine at Stockholm Söder Hospital we studied computerized records and discovered that 14% of those hospitalized patients who were on drug treatment for cardiovascular diseases were admitted due to problems or symptoms possibly caused by their drugs. Interactions were less common; the symptoms which warranted hospitalization were more often caused by additive pharmacological effects. Obviously, adverse effects of drugs decrease quality of life, cause unnecessary suffering and treatment, and are expensive for the health care system. Screening of computerized records helps us detect adverse effects, and facilitates prevention.

Fluvoxamine but not citalopram increases serum melatonin in healthy subjects-- an indication that cytochrome P450 CYP1A2 and CYP2C19 hydroxylate melatonin.

OBJECTIVE: The nocturnal serum melatonin (MT) level increases after ingestion of fluvoxamine (FLU)-- a selective serotonin re-uptake inhibitor (SSRI) with antidepressive properties. The mechanism behind the MT increase is unknown. Citalopram (CIT) is another SSRI. It is not known whether CIT affects the serum MT level. It may well be that these two compounds affect serum MT levels differently, inasmuch as the ways they inhibit cytochrome P450 (CYP) enzymes in the liver differ markedly. FLU inhibits CYP1A2 potently, and to some extent also CYP2C19, whereas CIT is without such an effect. CYP enzymes are probably involved in the hepatic metabolism of MT. If FLU, but not CIT, inhibits liver enzymes involved in the metabolism of MT, different serum MT concentrations should probably ensue. The objective of this investigation was to test this hypothesis. METHODS: Seven healthy subjects participated in three different experiments, which were performed in random order 6-8 days apart. In experiment A, placebo was given, in experiment B 40 mg CIT and in experiment C 50 mg FLU. All doses were given orally at 1600 hours. Serum MT concentrations were determined at regular intervals between 1600 hours and noon next day (20 h). Plasma concentrations of CIT were measured repeatedly in experiment B, and plasma FLU concentrations in experiment C. MT areas under the curve representing the 20-h period (MT-AUC(0-20)) were compared in the three experiments, and differences were statistically evaluated. RESULTS: FLU augmented the MT-AUC(0-20) by a factor of 2.8 compared with the effect of placebo (P < 0.01), whereas CIT was without significant effect. More MT was excreted in the urine after ingestion of FLU than after placebo. In contrast, CIT did not influence the MT excretion. A clear relationship was found between serum levels of MT and plasma concentrations of FLU. CONCLUSION: The serum MT level increased markedly after ingestion of FLU but not after CIT. The exact mechanism behind this finding is unknown, but decreased hepatic metabolism of MT by either CYP1A2 or CYP2C19, or both, is probable. Although exogenous MT, causing high MT concentration in plasma, has sleep-promoting properties in man, it is at this stage unknown whether serum MT concentrations in the range found in this study have similar effects. This has to be given further attention in additional studies.

Time course of enzyme induction in humans: effect of pentobarbital on nortriptyline metabolism.

To study the effect of induction we gave six male volunteers 10 mg nortriptyline three times a day for 4 weeks and 0.2 gm pentobarbital on days 8 to 21. Plasma and urinary levels of nortriptyline and metabolites were measured. The rate and extent of induction of the enzyme(s) were estimated by a model with use of nortriptyline concentrations. There was a marked decrease of nortriptyline levels after 2 days of pentobarbital treatment. Total clearance of nortriptyline increased more than twofold (range, 1.6-fold to 4.1-fold). Apparent metabolic clearance by 10-hydroxylation increased markedly. The decrease in nortriptyline levels was more rapid than the increase after pentobarbital cessation, fitting with the theory of the model. The induction of nortriptyline metabolism is probably mainly the result of an increase in a non-CYP 2D6 P450 isozyme, possibly CYP 3A4 or a CYP 2C form. More knowledge of induction characteristics of drugs should lead to better predictions of decreased effects and appearance of adverse effects. The kinetic model used for analysis of our data could then be useful.

Fibrinolytic treatment in suspected acute myocardial infarction--use and risks in clinical practice.

OBJECTIVES: To study the adherence to guidelines concerning fibrinolytic treatment of patients with suspected myocardial infarction and to obtain information on severe events in clinical practice. METHODS: Prospective reporting of all patients admitted for suspected acute myocardial infarction during 4 months in 1994 from 69 (73.4% of all) Swedish coronary care units. RESULTS: The study covers 10,652 admissions, representing 9726 patients. The mean percentage treated with fibrinolytic drugs of patients with a positive ECG (ST-elevation and/or bundle branch block), a delay < 12 h and no contraindications was 56%. The interhospital range was 18.1-94.1%. Fibrinolytic drugs were given with a delay time > 24 h in 12.5% of women and 15.7% of men, and 36.1% of patients with verified acute myocardial infarction were given fibrinolytic drugs. Streptokinase was used in 82.7% and alteplase in 15.5% of the patients, respectively (interhospital range 0-53.3%). CONCLUSIONS: Fibrinolytic therapy seems to be used in a non-rational way at several hospitals. Local quality systems may be a way to assure better care.

Influence of the dosing interval on prolactin release after remoxipride.

1. The prolactin response following administration of the D2-dopamine receptor antagonist remoxipride was studied in eight healthy male volunteers. The purpose of the study was to investigate the duration of a refractory period of prolactin release following two doses of remoxipride. A further aim was to compare the prolactin response following remoxipride and thyrotropin release hormone (TRH) during the refractory period. The subjects received two 30 min intravenous (i.v.) infusions of remoxipride 50 mg with different time intervals between the two doses, in a randomized six period crossover design. The time intervals between the two remoxipride doses were 2, 8, 12, 24 and 48 h. On one occasion the remoxipride dose was followed by an i.v. injection of TRH after 2 h. 2. The plasma peak prolactin concentrations obtained after the first remoxipride dose correspond to a maximal release of prolactin according to earlier studies. A small second peak of prolactin was observed after 2 h. The release was gradually increased with longer time intervals between the consecutive doses. The refractory period for a second prolactin release similar to the first one after remoxipride was found to be 24 h for most of the subjects. 3. TRH resulted in a faster and higher increase in prolactin response of a shorter duration than after remoxipride administered 2 h after the first dose.

Chlormethiazole as an efficient inhibitor of cytochrome P450 2E1 expression in rat liver.

Ethanol-inducible cytochrome P450 (CYP) 2E1 (CYP2E1) is responsible for the metabolism of many xenobiotics which exert toxic effects in humans. Specific inhibitors might constitute valuable tools in the elucidation of the pharmacological and toxicological roles of this isozyme in vivo. In the present investigation we have evaluated the effects of a drug used for treatment of ethanol withdrawal states, chloromethiazole (CMZ), on CYP2E1 expression in rat liver. A 4-fold induction of CYP2E1 was observed after 3 days of starvation, accompanied by a similar increase in the level of the corresponding mRNA. CMZ specifically inhibited the elevation of CYP2E1 mRNA and protein, but did not prevent CYP2B1 and CYP3A1 or CYP1A1 induction caused by treatment with phenobarbital or beta-naphthoflavone, respectively. From nuclear run-off experiments it was apparent that the rate of the CYP2E1 gene transcription was inhibited greatly by CMZ treatment. Rats treated with ethanol in a total enteral nutrition model had higher CYP2E1-dependent hepatic microsomal activities of p-nitrophenol hydroxylase and carbon tetrachloride-induced lipid peroxidation than controls, and simultaneous CMZ treatment abolished the ethanol-dependent induction. In vitro experiments with rat liver microsomes showed that CMZ did not act as an inhibitor of CYP2E1-dependent catalytic activities or as an inhibitor of microsomal NADPH and CYP2E1-dependent lipid peroxidation. In conclusion, we suggest that CMZ might constitute an efficient and specific inhibitor of CYP2E1 expression suitable for in vivo experiments.

Interaction study between remoxipride and biperiden.

Twelve healthy male volunteers took part in a double-blind randomised cross-over study composed of three treatment sessions: remoxipride 100 mg; remoxipride 100 mg plus biperiden 4 mg; and biperiden 4 mg. Plasma and urine concentrations of remoxipride and biperiden, plasma prolactin levels, salivary flow and adverse events were recorded to assess pharmacodynamic interactions. Remoxipride and biperiden had no effect on each other's plasma concentrations. Biperiden did not affect the urinary recovery or renal clearance of remoxipride. Prolactin levels were unaffected by biperiden but increased following remoxipride administration. Differences in prolactin Cmax and tmax following remoxipride versus concomitant (remoxipride + biperiden) treatment were not statistically significant. However, a slight but statistically significant (P = 0.04) increase in prolactin AUC was observed after concomitant treatment. No significant differences could be observed between the recorded salivary flow in all the treatment sessions. Single doses of remoxipride and biperiden showed no pharmacokinetic or pharmacodynamic interaction.

Different regiospecificity in the hydroxylation of the antidepressant desmethylimipramine between rat brain and liver.

Incubation of the tricyclic antidepressant desmethylimpramine (DMI) with rat liver or brain microsomes in the presence of NADPH or t-butyl-hydroperoxide (TBH) revealed different regiospecificities in the hydroxylation reactions between the tissues. In brain preparations 10-OH-DMI was formed in reactions supported by NADPH or TBH, whereas in the latter case also an unidentified metabolite could be detected. Inclusion of exogenous NADPH-cytochrome P450 reductase in the brain preparations caused a 10-fold higher rate of 10-hydroxylation but no 2-OH-DMI could be detected. By contrast, liver microsomal preparations in the presence of NADPH catalyzed formation of both 2- and 10-OH-DMI, whereas only 10-OH-DMI was formed in TBH-supported reactions. The results indicate that antidepressant drugs can be metabolized in brain with different stereospecificity as compared to liver.

Plasma levels of thioridazine and metabolites are influenced by the debrisoquin hydroxylation phenotype.

The pharmacokinetics of thioridazine and its metabolites were studied in 19 healthy male subjects: 6 slow and 13 rapid hydroxylators of debrisoquin. The subjects received a single 25 mg oral dose of thioridazine, and blood samples were collected during 48 hours. Concentrations of thioridazine and metabolites in serum were measured by HPLC. Slow hydroxylators of debrisoquin obtained higher serum levels of thioridazine with a 2.4-fold higher Cmax and a 4.5-fold larger AUC(0-infinity) associated with a twofold longer half-life compared with that of rapid hydroxylators. The side-chain sulphoxide (mesoridazine) and sulphone (sulphoridazine), which are active metabolites, appeared more slowly in serum and had lower Cmax values, but comparable AUC. The thioridazine ring-sulphoxide attained higher Cmax and 3.3-fold higher AUC in slow hydroxylators than in rapid hydroxylators of debrisoquin. Thus the formation of mesoridazine from thioridazine and the 4-hydroxylation of debrisoquin seem to be catalyzed by the same enzyme, whereas the formation of thioridazine ring-sulphoxide is probably formed mainly by another enzyme.

Neuroendocrine responses to single oral doses of remoxipride and sulpiride in healthy female and male volunteers.

Six female and six male healthy volunteers received 100 mg remoxipride, 200 mg sulpiride and placebo as single oral doses in a double blind trial with a randomized crossover design. The main objective was to compare the effect of the two drugs on serum prolactin levels, but effects on other hormones were also investigated. Remoxipride and sulpiride increased the serum levels of prolactin to similar peak levels. This effect was larger in female than in male subjects. Sulpiride increased prolactin levels at much lower plasma concentrations than remoxipride, and sulpiride's effect on prolactin lasted for considerably longer than remoxipride's. No consistent effects on serum levels of LH, FSH, GH, oestradiol, progesterone, testosterone or cortisol could be detected after remoxipride and sulpiride compared to placebo. No drug-related effects on plasma homovanillic acid (HVA) were found.

Pharmacokinetics and effects on prolactin of remoxipride in patients with tardive dyskinesia.

The pharmacokinetics of remoxipride, a new selective dopamine-D2 receptor antagonist with antipsychotic action, was evaluated in eight elderly psychiatric patients with tardive dyskinesia (TD). The daily oral doses of remoxipride were gradually increased from 50 mg per day to 200 mg t.i.d. over 2 weeks. The pharmacokinetics following the initial 50 mg dose (day 1) and the last 200 mg dose (day 15) of the drug were compared in serial samples. Plasma prolactin concentrations were assessed at the same time points. The area under the total plasma concentration versus time curves (AUC) of remoxipride increased proportionally with dose from day 1 to 15. The mean "dose corrected" AUC values for the total concentrations were 96.8 at day 1 (4 X 24.2, 50 mg single oral dose) and 92.2 mumol.h/l at day 15 (200 mg). The unbound fraction of remoxipride calculated on AUC was slightly higher on day 15 (20%) than on day 1 (15%) (P less than 0.05), indicating slightly concentration-dependent protein binding of the drug. The mean elimination half-life of total remoxipride was slightly longer on day 15 than day 1 (7.5 versus 5.3 h, P less than 0.01) The corresponding half-lives for the unbound concentrations were 6.4 and 3.9 h, respectively (P less than 0.01). The pharmacokinetics of remoxipride is similar in these TD patients and in non-TD patients in previous studies. Following repeated administration of remoxipride, tolerance to the prolactin-releasing action of remoxipride is observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucuronidation of codeine and morphine in human liver and kidney microsomes: effect of inhibitors.

Glucuronidation of codeine was detected and compared with that of morphine in microsomes from human livers and kidneys. Vmax values for codeine-6-glucuronide (C6G) were 0.54 +/- 0.24 and 0.74 +/- 0.35 nmol/mg/min. in the livers and 0.10 and 0.13 nmol/mg/min. in the kidney, respectively, when codeine and UDP-glucuronic acid (UDPGA) were incubated with microsomal preparation. The corresponding Km values were 2.21 +/- 0.68 and 1.41 +/- 0.36 mM in the livers and 6.69 and 4.12 mM in the kidney. The average codeine glucuronyltransferase (GT) activity was 14-fold lower in the six kidneys than in the 11 livers. Higher GT activities were observed in liver microsomes from patients who had been exposed to enzyme inducers. Rates of glucuronide formation from morphine correlated significantly with those from codeine in both human liver and kidney microsomes. Morphine, amitriptyline, diazepam, probenecid and chloramphenicol inhibited codeine glucuronidation with Ki values of 3.6, 0.13, 0.18, 1.7 and 0.27 mM, respectively.

[Remoxipride, a selective antagonist of dopamine D2 receptors, in the treatment of delusional psychoses]. / Rémoxipride, antagoniste sélectif des récepteurs dopaminergiques D2, dans le traitement des psychoses délirantes.

Remoxipride, a substituted benzamide, is a new antipsychotic agent which differs from classical neuroleptics in several ways. It has a selective action on the dopamine D2 receptors in the brain and little effect on a variety of other receptor types including serotonin, noradrenaline, acetylcholine and histamine receptors. This implies advantages over classical neuroleptics which have less selective modes of action and subsequently increased propensities to cause side effects. The pharmacokinetics of remoxipride are uncomplicated. The drug is rapidly absorbed, plasma levels increase with dose, and elimination is via urinary excretion. No clinically significant drug interactions have been found. Remoxipride has been shown to be as effective in the treatment of schizophrenic patients as haloperidol in both short and long term double-blind trials. Both positive and negative symptoms are improved. However, remoxipride shows advantages over haloperidol in that the incidences of extrapyramidal symptoms and increased plasma prolactin concentrations are lower in remoxipride recipients. There are no clinically relevant adverse effects on chemistry, haematology or cardiovascular variables.

Clinical pharmacokinetics of remoxipride.

The clinical pharmacokinetics of remoxipride, a pure enantiomer, have been studied in healthy volunteers and patients. After oral administration the drug is rapidly and almost completely absorbed with a bioavailability above 90%. Thus remoxipride is a low clearance drug, with a systemic plasma clearance of about 120 ml/min, and without any first-pass metabolism. The apparent volume of distribution is 0.7 1/kg, about 80% being bound to plasma proteins (mainly alpha 1-acid glycoprotein). Remoxipride has a plasma half-life in the range of 4-7 h and is eliminated by both hepatic metabolism and renal excretion. Slightly more than 70% of the dose is recovered as urinary metabolites and about 25% is excreted unchanged. Steady-state plasma levels are reached within 2 days, and they increase linearly with doses up to 600 mg daily. There is no evidence that active metabolites of remoxipride are present in the blood. Decreased renal function is associated with increased levels of remoxipride, whereas moderate cirrhosis of the liver only slightly affects elimination. There are no pharmacokinetic interactions between remoxipride and diazepam, ethanol, biperiden, or warfarin.