A common X-linked inborn error of carnitine biosynthesis may be a risk factor for nondysmorphic autism.

We recently reported a deletion of exon 2 of the trimethyllysine hydroxylase epsilon (TMLHE) gene in a proband with autism. TMLHE maps to the X chromosome and encodes the first enzyme in carnitine biosynthesis, 6-N-trimethyllysine dioxygenase. Deletion of exon 2 of TMLHE causes enzyme deficiency, resulting in increased substrate concentration (6-N-trimethyllysine) and decreased product levels (3-hydroxy-6-N-trimethyllysine and γ-butyrobetaine) in plasma and urine. TMLHE deficiency is common in control males (24 in 8,787 or 1 in 366) and was not significantly increased in frequency in probands from simplex autism families (9 in 2,904 or 1 in 323). However, it was 2.82-fold more frequent in probands from male-male multiplex autism families compared with controls (7 in 909 or 1 in 130; P = 0.023). Additionally, six of seven autistic male siblings of probands in male-male multiplex families had the deletion, suggesting that TMLHE deficiency is a risk factor for autism (metaanalysis Z-score = 2.90 and P = 0.0037), although with low penetrance (2-4%). These data suggest that dysregulation of carnitine metabolism may be important in nondysmorphic autism; that abnormalities of carnitine intake, loss, transport, or synthesis may be important in a larger fraction of nondysmorphic autism cases; and that the carnitine pathway may provide a novel target for therapy or prevention of autism.

Epidemiological study of urinary 6beta-hydroxycortisol to cortisol ratios and breast cancer risk.

The ratio of urinary 6beta-hydroxycortisol:cortisol is a measure of the activity of cytochrome p450 3A4 (CYP3A4). CYP3A4 catalyzes the formation of the genotoxic estrogen, 16alpha-hydroxyestrone. It is also involved in the activation of many other mammary carcinogens, such as the polycyclic aromatic hydrocarbons and heterocyclic amines. We evaluated the association between urinary cortisol ratios and breast cancer risk in a subgroup of women who participated in a population-based case-control study in Shanghai. Overnight urine samples from 246 case-control pairs were assayed for 6beta-hydroxycortisol (6beta-OHC) to cortisol. The urine samples from all of the breast cancer patients were collected before any chemotherapy or radiotherapy. In-person interviews were conducted to obtain comprehensive information on dietary habits, reproductive history, and other lifestyle factors. The median levels of 6beta-OHC:cortisol ratios were 2.61 in cases and 2.16 in controls, a 20.8% difference (P < 0.001). The case-control difference was larger in women over 45 years of age (31.3% difference; P < 0.001) than younger women (6.0%; P = 0.45). After adjusting for confounding variables, the risks of breast cancer were increased from 1.0 (reference) to 1.6 [95% confidence interval (CI), 0.9-3.1], 2.2 (95% CI, 1.1-4.2), and 3.7 (95% CI, 1.9-7.4; P for trend, <0.001) with increasing levels of 6beta-OHC:cortisol ratios. The positive association was more pronounced among older women (>45 years) than among younger women (< or = 45 years). The adjusted odds ratios associated with the highest cortisol ratio were 6.0 (95%CI, 2.2-16.1) among older women and 2.2 (95%CI, 0.8-6.1) among younger women. The association of the 6beta-OHC:cortisol ratio was stronger among older women who had a high body mass index, late age at menopause, and early age at menarche (factors related to high endogenous estrogen exposure) than those who did not have these factors. These findings are consistent with the role of CYP3A4 in estrogen and carcinogen metabolism and suggest that high CYP3A4 activity may be a risk factor for breast cancer risk.

Fluoxetine pharmacokinetics and effect on CYP2C19 in young and elderly volunteers.

The objective of this study was to assess in both young and elderly volunteers the pharmacokinetics of fluoxetine and norfluoxetine and effects on cytochrome P450 (CYP) 2C19. Male volunteers aged 18 to 40 years (N = 14) or older than 65 years (N = 16) received fluoxetine 20 mg/day for 6 weeks and fluoxetine 40 mg/day for an additional 6 weeks. Blood was drawn over a 24-hour period after the initial dose and after 6 weeks and 12 weeks to determine AUC0-24, Cmax, and tmax; weekly to evaluate predose levels (C0); and over a 3-week period after discontinuation to evaluate washout (t1/2). Mephenytoin was used to assess CYP2C19 activity before and after 6 weeks and 12 weeks of fluoxetine. Fluoxetine AUC0-24, C0, and Cmax did not differ in young and elderly subjects. The norfluoxetine C0 was 22% lower in elderly subjects (p < .05), with comparable decreases in AUC0-24 and Cmax. In the elderly volunteers, the t1/2 for fluoxetine was 25% longer (5.0 vs. 4.0 days) and for norfluoxetine was 33% longer (20 vs. 15 days), although variability and sample size precluded statistical significance. Fluoxetine dosing inhibited CYP2C19 activity in both age groups, increasing the (S)- to (R)-mephenytoin ratio 3- to 4-fold (p < .01). The half-lives of fluoxetine and norfluoxetine at 40 mg/day were longer than commonly reported in the literature and may be longer in elderly subjects. Fluoxetine substantially inhibited the metabolism of the CYP2C19 substrate (S)-mephenytoin.

Determination of S/R ratio of mephenytoin in human urine by chiral HPLC and ultraviolet detection and its comparison with gas chromatography.

AIM: To improve HPLC method for rapid determination of urinary S/R-ratio of mephenytoin, a widely used metabolic index for cytochrome P-450 2C19 (CYP2C19) activity. METHODS: Aliquots of 0-8-h urine sample after dosing racemic mephenytoin 100 mg underwent one-step extraction with dichloromethane. Analysis was performed on a chiral column (250 mm x 4 mm, 5 microns) at lambda = 207 nm. The eluent was a mixture of acetronitrile and water containing both 0.1% glacial acetic acid and 0.2% triethylamine (14:86, vol/vol) at a flow-rate of 0.9 mL.min-1. RESULTS: The enatiomers of mephenytoin in urine were well separated within 9 min. A linear correlation was observed between 50-5000 micrograms.L-1 with the detection limit of 12.5 micrograms.L-1 for both enantiomers of mephenytoin. This HPLC analysis was comparable to gas chromatography in accuracy and sensitivity, but with much shorter retention time and better resolution. CONCLUSION: The present HPLC method is good for rapid determination of the ability of subjects to hydroxylate S-mephenytoin after oral administration of the racemic drug.

Lack of effect of chloroquine on the debrisoquine (CYP2D6 and S-mephenytoin (CYP2C19) hydroxylation phenotypes.

The effects of chloroquine (CHQ) on debrisoquine hydroxylase (CYP2D6) and S-mephenytoin hydroxylase (CYP2C19) were assessed in 11 black Zimbabwean and 12 white Swedish healthy volunteers. The activity of CYP2D6 was measured as the urinary debrisoquine to 4-hydroxydebrisoquine metabolic ratio and that of CYP2C19 as the urinary S- to R-mephenytoin enantiomer ratio (S/R). There were no statistically significant differences in either metabolic ratio as a result of prophylactic or loading doses of CHQ. This indicates that CHQ does not inhibit CYP2D6 or CYP2C19 in vivo and is unlikely to compromise the metabolism of substrates for these two enzymes. It is, therefore, also unlikely that residual CHQ in populations under study will interfere with phenotyping of either CYP2D6 or CYP2C19.

Effects of omeprazole and cimetidine on the urinary metabolic ratio of proguanil in healthy volunteers.

OBJECTIVE: To examine the effects of omeprazole and cimetidine on the urinary recovery and metabolic ratio of proguanil in healthy subjects. METHODS: A metabolic interaction study was conducted in 12 young, healthy extensive metabolisers of proguanil, a CYP2C19 substrate, following a single 100 mg oral dose by analysis of urine collected for 8 hours. RESULTS: Concomitant administration of omeprazole (20 mg), a CYP2C19 substrate, had no significant effect on the urinary recovery of proguanil or cycloguanil, or the ratio of cycloguanil to proguanil [mean 0.76 (95% CI: 0.53 to 0.98) proguanil alone; mean 0.65 (95% CI: 0.40 to 0.89) proguanil plus omeprazole]. In contrast, cimetidine (400 mg), a general CYP inhibitor and renal organic cation secretion inhibitor, decreased the urinary recovery of cycloguanil and reduced the metabolic ratio from a mean of 0.76 to 0.54 (P < 0.01). In 3 poor metabolisers of proguanil, cimetidine had no effect on the proguanil metabolic ratio. CONCLUSION: The concomitant administration of omeprazole or cimetidine will not result in phenocopying extensive metabolisers of proguanil, although cimetidine inhibits the formation of cycloguanil in extensive metabolisers.

Metabolic interactions of methoxsalen and coumarin in humans and mice.

Methoxsalen (8-methoxypsoralen) is a very potent inhibitor of human cytochrome P450 2A6 (CYP2A6) and mouse Cyp2a-5-mediated coumarin 7-hydroxylation in vitro. To determine the effect of methoxsalen on coumarin 7-hydroxylation in humans in vivo, five subjects were given 45 mg of methoxsalen and 5 mg of coumarin. Methoxsalen inhibited in vivo coumarin metabolism by 47 +/- 9.2% (mean +/- SEM). Methoxsalen was metabolized in human liver microsomes at the rate of 50-100 pmol/mg protein/min (approx. 30% of the activity in mouse liver microsomes). Metabolism was not inhibited by the anti-Cyp2a-5 antibody in human liver microsomes. NIH 3T3 cells stably expressing catalytically active CYP2A6 enzyme did not metabolize methoxsalen, indicating that CYP2A6 does not accept methoxsalen as a substrate. In pyrazole-induced mouse liver microsomes, methoxsalen metabolism was inhibited by the anti-Cyp2a-5 antibody. Cyp2a-5 protein expressed in the yeast Saccharomyces cerevisiae was capable of metabolizing methoxsalen, indicating that methoxsalen is a substrate of Cyp2a-5. Although kinetic studies indicated that the inhibition of coumarin 7-hydroxylation by methoxsalen is competitive in human liver microsomes, methoxsalen does not appear to be a substrate for CYP2A6. Methoxsalen and coumarin have the potential of strong metabolic interactions in man.

Role of cytochrome P4502D6 in the metabolism of brofaromine. A new selective MAO-A inhibitor.

The metabolic fate of brofaromine (CGP 11 305 A), a new, reversible, selective MAO-A inhibitor, has been assessed in poor (PM) and extensive (EM) metabolizers of debrisoquine. Compared to EM, PM had significantly longer t1/2 (136%) and larger AUC(0-infinity) (110%) of the parent compound brofaromine and a lower Cmax (69%) and AUC (0-72 h) (40%) of its O-desmethyl metabolite. The mean metabolite/substrate ratio (based on urine excretion) was about 6-times greater in EM than in PM. Treatment with quinidine converted all EM into phenocopies of PM. All pharmacokinetic parameters of brofaromine and O-desmethyl-brofaromine in EM treated with quinidine were similar to those of untreated PM, including the metabolite/substrate ratio. Quinidine treatment of PM did not alter the pharmacokinetics of brofaromine or of its metabolite, nor the metabolite/substrate ratio. The results indicate a role for the debrisoquine type of oxidation polymorphism in the O-demethylation and pharmacokinetics of brofaromine.

[15N]methacetin urine test to measure liver function: methodology for application in pediatrics.

A simple, noninvasive test is proposed to measure the activity of the hepatocellular monooxygenase system in vivo. Elimination rates of the stable isotope 15N are measured in urine after an oral dose of the 15N-labeled phenacetin homologue [15N]methacetin. Different forms of obtaining and expressing results are investigated in order to determine optimum methodology and differentiation for clinical application in pediatrics. The best discriminating power and reliability of results are seen with the measurement of 15N elimination half-life. For follow-up, a more easily measured parameter--eliminated dose over 9 h--is sufficient. In the latter case, only total nitrogen and 15N contents of a collective urine sample are measured.

11 Beta-hydroxylase deficiency congenital adrenal hyperplasia: update of prenatal diagnosis.

Hormonal measurements in maternal urine and amniotic fluid (AF) during pregnancy and/or at delivery correctly predicted the postnatal diagnosis of 11 beta-hydroxylase deficiency congenital adrenal hyperplasia (11 beta-OH deficiency CAH) in 7 fetuses at risk. In the 4 affected ones, maternal urinary tetrahydro-11-deoxycortisol (THS) excretion was high during the first trimester [0.3-2.2 mg/day (1.1-7.7 mumol/day)] and rose further during the third trimester [0.5-3.5 mg/day (1.8-12.3 mumol/day)] compared to urinary THS excretion in 20 normal pregnancies of the same gestational age (P less than 0.01). In 1 mother, dexamethasone administration (2 mg/day for 72 h) greatly reduced urinary THS excretion (and plasma steroid levels). Urinary THS excretion was low after delivery in these mothers, in normal pregnancies, and in parents of affected individuals [less than 0.05 mg/day (less than 0.08 mumol/day); P = NS]. However, 2 of the 3 heterozygous mothers who carried nonaffected fetuses excreted moderately increased amounts of THS during pregnancy, ranging from 0.15-0.26 mg/day (0.53-0.91 mumol/day), significantly higher than normal (P less than 0.01). Although urinary THS excretion in these mothers was similar to that in 2 mothers with affected fetuses early in pregnancy, urinary THS excretion was higher in mothers with affected compared to those with nonaffected fetuses after the first trimester (P less than 0.01). AF THS and 11-deoxycortisol concentrations were markedly elevated in pregnancies with affected fetuses (P less than 0.01), but normal in nonaffected ones. AF delta 4-androstenedione levels were high in 2 pregnancies and borderline elevated in a third. Although the AF tetrahydrocortisol and tetrahydrocortisone levels were always within the normal range, the AF THS to tetrahydrocortisol plus tetrahydrocortisone ratio was significantly elevated in all pregnancies with affected fetuses (2.8-5.5; P less than 0.01) and normal in nonaffected ones (0.48-1.2; P = NS) compared to that in 160 normal pregnancies [0.64 +/- 0.34 (+/- SD)]. AF 17-hydroxyprogesterone, testosterone, and 11-deoxycorticosterone levels were normal in all pregnancies. Maternal plasma 11-deoxycortisol and delta 4-androstenedione concentrations, determined sequentially throughout gestation, were variable and did not contribute to prenatal diagnosis. All affected infants were born hyperpigmented, 2 were large for gestational age, and the female was severely virilized. In the first week of life 2 males developed severe hypertension with seizures and adrenal insufficiency, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Fluorescence high performance liquid chromatographic determination of 3 alpha-hydroxysteroids in urine of 21-hydroxylase deficiency.

A fluorescence high performance liquid chromatographic method using an immobilized 3 alpha-hydroxysteroid dehydrogenase column as a post-column enzymatic reactor was developed for the determination of corticosteroid metabolites in the urine of subjects with congenital adrenal hyperplasia. 3 alpha-Hydroxysteroids, such as pregnanetriol, pregnanediol and pregnanetriolone, in the eluate from mu-Bondapak phenyl column (300 x 3.9 mm I.D.) using 0.05% ammonium phosphate buffer (pH 7.1)-acetonitrile-methanol (100:55:15) as the mobile phase was mixed with NAD+ solution in the enzyme column at 30 degrees C to generate NADH, which was monitored by a fluorophotometric detector. Each steroid was measured at the 2.5 micrograms/dl at the highest sensitivity of the detector. The mean recoveries and reproducibilities were 91.5-108.2% with 0.9-6.5% (CV%).

Alterations of the tryptophan--nicotinic acid metabolism in vitiligo.

Tryptophan metabolism "via kynurenine" is altered in vitiligo: after a load of the amino acid the urinary excretion of 3-hydroxykynurenine and 3-hydroxyanthranilic acid is decreased, whereas that of xanthurenic acid and its 8-methyl ether is increased. The excretory values of the metabolites suggest a deficiency of the activity of kynurenine hydroxylase and kynunerinase, the enzymes involved in the metabolism of 3-hydroxykynurenine and 3-hydroxyanthranilic acid. The reduced excretion of 3-hydroxykynurenine, a tryptophan metabolite involved in melanin biosynthesis, may indicate a smaller utilization of tryptophan in the biogenesis of the melanins.