Biomedical subjects

Yuen Yi Hon

Publications and source records attributed to Yuen Yi Hon.

8 recordsLinked to original sources

PubMed2006

Endogenous histamine and cortisol levels in subjects with different histamine N-methyltransferase C314T genotypes : a pilot study.

BACKGROUND: Histamine N-methyltransferase (HNMT) catalyzes the methylation of histamine and plays an important role in histamine biotransformation in bronchial epithelium. Enzymatic activity of HNMT has been shown to be regulated by genetic factors, including polymorphisms in the HNMT gene. In this pilot study we determined endogenous levels of histamine and cortisol in plasma and whole blood samples from subjects with different genotypes for the HNMT C314T polymorphism, and investigated whether these parameters differed between individuals with the HNMT CC genotype and those with the CT genotype. METHODS: Blood samples were collected from 48 unrelated volunteers (36 males, 12 females), aged 21-40 years, who participated in the study. PCR-restriction fragment length polymorphism analysis was used to determine HNMT C314T genotypes. Erythrocyte HNMT activity was determined as well as plasma and whole blood levels of histamine and cortisol. Two-group comparisons of the various parameters were analyzed by Blocked Wilcoxon test and Wilcoxon Rank Sum test as appropriate. RESULTS: Thirty-seven subjects (24 Caucasians, three African Americans, one Middle Eastern, five Indians, three Chinese, and one Filipino) were found to have the homozygous CC genotype. Ten subjects (eight Caucasians, one Middle Eastern, and one Chinese) were heterozygous and one individual (Pakistani) was homozygous for the variant 314T allele. The frequency of HNMT CT heterozygotes in the small Caucasian cohort was 0.125. Median enzyme activity was significantly lower in subjects with the heterozygous CT genotype than in those with the homozygous CC genotype (485 vs 631 U/mL of red blood cells; p=0.023). A broad range of histamine levels in plasma and whole blood was observed for all subjects. Whereas the median plasma histamine level was found to be higher in heterozygotes for the wild-type 314C allele than homozygotes (3.32 vs 2.30 nmol/L; p=0.021), there was no difference between the two groups in histamine levels in whole blood. Cortisol levels were similar between individuals with the homozygous CC genotype and those with the heterozygous CT genotype. CONCLUSION: Wide variability of plasma and whole-blood histamine levels was observed in subjects with different HNMT C314T genotypes. Endogenous levels of histamine are likely to be affected by various genes and polymorphisms.

Adult↗

PubMed2006

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism.

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Adult↗

PubMed2006

Reduced methylprednisolone clearance causing prolonged pharmacodynamics in a healthy subject was not associated with CYP3A5*3 allele or a change in diet composition.

The influence of diet and genetics was investigated in a healthy white person who had distinctly low methylprednisolone clearance. Pharmacokinetic and pharmacodynamic parameter values were similar on 2 occasions during the consumption of a low-carbohydrate diet and a Weight Watchers diet, indicating that the decreased clearance was unlikely attributable to a change in diet composition. Although the subject was found to be homozygous for CYP3A5*3, genetic findings were not significant for a number of other CYP3A4 and CYP3A5 allelic variants. Because of the high prevalence of CYP3A5*3/*3 in whites and because 5 of 7 white control subjects are also homozygous for CYP3A5*3, this genotype cannot fully explain the reduced metabolism of the drug. Other genetic or contributing factors might have been involved. New polymerase chain reaction-based genotyping methods for functionally defective CYP3A5*6, *8, *9, and *10 alleles were developed in this study. These assays will be useful for CYP3A5 genotype analysis in future clinical studies.

Adult↗

PubMed2006

Lack of pharmacokinetic interaction between lamotrigine and olanzapine in healthy volunteers.

STUDY OBJECTIVE: To investigate the potential drug-drug interaction between lamotrigine, an antiepileptic agent used to treat bipolar disorders, and olanzapine, an atypical antipsychotic drug also used to treat bipolar disorders, both of which are metabolized by the uridine diphosphate glucuronosyltransferase system. DESIGN: Prospective cohort study. SETTING: University center for clinical research. SUBJECTS: Fourteen nonsmoking, healthy volunteers. INTERVENTION: Subjects received lamotrigine 25 mg/day for 5 days, then 50 mg/day for 10 days to achieve steady-state concentrations. On day 15, blood samples were obtained before and 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours after the dose. Lamotrigine 50 mg/day was then given for an additional 3 days. On the next day, lamotrigine 50 mg and olanzapine 5 mg were coadministered. Blood samples were obtained at the same times as before and at 48, 72, and 96 hours after dosing. MEASUREMENTS AND MAIN RESULTS: Blood samples were assayed for lamotrigine and olanzapine concentrations by means of high-performance liquid chromatography. Olanzapine did not significantly affect lamotrigine disposition, as we observed no differences in the area under the concentration-time curve from 0-24 hours or in lamotrigine plasma concentrations at baseline or at 24 hours. For lamotrigine, the mean time to reach maximum concentration was significantly prolonged during olanzapine coadministration (mean +/- SD 1.9 +/- 1.3 vs 4.0 +/- 3.0 hrs, p = 0.025), possibly because of the anticholinergic properties associated with olanzapine. Mild sedation was the only adverse effect that occurred during lamotrigine and olanzapine coadministration. CONCLUSION: Lamotrigine and olanzapine can safely be combined in healthy volunteers at the low doses studied, without a clinically significant interaction. When prescribing high doses of olanzapine and lamotrigine for bipolar disorder, patients must be carefully monitored.

Adult↗

PubMed2004

Development of capillary zone electrophoresis-electrospray ionization-mass spectrometry for the determination of lamotrigine in human plasma.

A method of coupling capillary zone electrophoresis (CZE) with electrospray ionization-mass spectrometry (ESI-MS) detection has been developed for monitoring an antiepileptic drug, lamotrigine (LTG) in human plasma. The CZE-MS was developed in three stages: (i) CZE separation and ESI-MS detection of LTG and tyramine (TRM, internal standard) were simultaneously optimized by studying the influence of CZE background electrolyte (BGE) pH, BGE ionic strength, and nebulizer pressure of the MS sprayer; (ii) sheath liquid parameters, such as pH, ionic strength, organic modifier content, and flow rate of the sheath liquid, were systematically varied under optimum CZE-MS conditions developed in the first stage; (iii) MS sprayer chamber parameters (drying gas temperature and drying gas flow rate) were varied for the best MS detection of LTG. The developed assay was finally applied for the determination of LTG in plasma samples. The linear range of LTG in plasma sample assay was between 0.1-5.0 microg/mL with a limit of detection as low as 0.05 microg/mL and run time less than 6 min. Finally, the concentration-time profile of LTG in human plasma sample was found to correlate well when CZE-ESI-MS was compared to a more established method of high-performance liquid chromatography with ultraviolet detection.

Anticonvulsants↗

PubMed2004

CYP2C9 genetic polymorphisms and warfarin.

The objective of this study was to report 2 cases of CYP2C9 genetic polymorphism and elevated warfarin S:R ratios in patients taking low doses of warfarin, and compare the observed characteristics with those in published reports. Two patients of different age groups and races were evaluated for CYP2C9 genotype and warfarin S:R ratios. The patients had been stabilized on weekly warfarin doses of 10.5 mg and 10 mg, respectively. Each patient was found to have at least 1 variant CYP2C9 allele. Elevated warfarin S:R ratios in both patients provided evidence for impaired metabolism of S-warfarin. This report of a CYP2C9*3 heterozygous individual taking a low dose of warfarin is consistent with previous reports in the literature. This summary of a CYP2C9*6 homozygous individual taking a low dose of warfarin is the first such published report. CYP2C9 genotyping in these patients provided a likely explanation for their continued low warfarin dosage requirements. Awareness of a patient's CYP2C9 genotype may provide an explanation for low warfarin dosage requirements in stable patients and may help in determining the optimal dose in patients being initiated on warfarin.

Adult↗

PubMed2002

Influence of ritonavir on olanzapine pharmacokinetics in healthy volunteers.

HIV infection and psychotic illnesses frequently coexist. The atypical antipsychotic olanzapine is metabolized primarily by CYP1A2 and glucuronosyl transferases, both of which are induced by the HIV protease inhibitor ritonavir. The purpose of this study was to determine the effect of ritonavir on the pharmacokinetics of a single dose of olanzapine. Fourteen healthy volunteers (13 men; age range, 20-28 years) participated in this open-label study. Subjects received olanzapine 10 mg and blood samples were collected over a 120-hour post-dose period. Two weeks later, subjects took ritonavir 300 mg twice daily for 3 days, 400 mg twice daily for 4 days, and 500 mg twice daily for 4 days. The next morning, after 11 days of ritonavir, olanzapine 10 mg was administered and blood sampling was repeated. Plasma samples were analyzed for olanzapine with HPLC. We compared olanzapine noncompartmental pharmacokinetic parameter values before and after ritonavir with a paired Student t test. Ritonavir reduced the area under the plasma concentration-time curve of olanzapine from 501 ng. hr/mL (443-582) to 235 ng. hr/mL (197-294) (p < 0.001), the half-life from 32 hours (28-36) to 16 hours (14-18) (p = 0.00001), and the peak concentration from 15 ng/mL (13-19) to 9 ng/mL (8-12) (p = 0.002). Olanzapine oral clearance increased from 20 L/hr (18-23) to 43 L/hr (38-51) (p < 0.001) after ritonavir. Ritonavir significantly reduced the systemic exposure of olanzapine in volunteers. Patients receiving this combination may ultimately require higher olanzapine doses to achieve desired therapeutic effects.

Adult↗

PubMed2002

Effect of Seville orange juice and grapefruit juice on indinavir pharmacokinetics.

Considerable interpatient variability in indinavir pharmacokinetics, possibly due in part to variable metabolism of the drug through intestinal cytochrome P450 (CYP) 3A4, may contribute to poor virologic response in certain individuals with HIV infection. The purpose of this study was to characterize the influence of intestinal CYP3A4 modulation with grapefruit juice and Seville orange juice on indinavir pharmacokinetics. In an open-label, three-period crossover study, 13 healthy volunteers received indinavir 800 mg every 8 hours for 1 day and a single 800 mg dose the next morning. The last two indinavir doses were taken with 8 ounces of Seville orange juice, single-strength grapefruit juice, or water (control). Plasma samples were collected at time 0 (predose) and at 0.5, 1, 2, 3, 4, and 5 hours after the last indinavir dose. Concentration-time data were analyzed using noncompartmental methods. Coadministration of Seville orange juice and indinavir resulted in a statistically significant increase in indinavir t(max) (1.87 [1.65-2.22] vs. 1.25 [1.03-1.60] h; p < 0.05) without altering other pharmacokinetic parameter values. Grapefruit juice administration did not result in any changes in indinavir pharmacokinetics. Modulation of intestinal CYP3A4 by grapefruit juice and Seville orange juice did not alter the systemic availability of indinavir. The contribution of presystemic metabolism to indinavir interpatient variability appears to be small.

Adult↗