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Ryuya Horiuchi

Publications and source records attributed to Ryuya Horiuchi.

At least 19 recordsLinked to original sources
PubMed2006

A novel intronic mutation that may affect genotyping result of CYP2C8 by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) is strongly associated with CYP2C8*3 in a South American population.

During the investigation of a CYP2C8*3 genetic polymorphism in a South American population, we obtained a discrepant result using two different polymerase chain reaction (PCR) protocols. A single nucleotide polymorphism (SNP) (IVS3+43 G>C) was identified in the intron 3 region, which was used as a primer-annealing site of one of the two PCR protocols. A genotyping method was developed to enable discrimination of the CYP2C8*1A, CYP2C8*3 (416 G>A), and CYP2C8*3 (416G>A; IVS3+43 G>C) alleles. In a screen of a South American population, we found that individuals carrying the CYP2C8*3 (416 G>A) polymorphism also carried the CYP2C8*3 (416G>A; IVS3+43 G>C). However, we did not find any carriers of CYP2C8*3 (416G>A; IVS3+43 G>C) in a Japanese population.

Aryl Hydrocarbon Hydroxylases↗
PubMed2006

Prediction of total propofol clearance based on enzyme activities in microsomes from human kidney and liver.

OBJECTIVE: Propofol is commonly used for anesthesia and sedation in intensive care units. Approximately 53% of injected propofol is excreted in the urine as the glucuronide and 38% as hydroxylated metabolites. Liver, kidneys and intestine are suspected as clearance tissues. We investigated the contribution of the liver and kidneys to propofol metabolism in humans using an in vitro-in vivo scale up approach. METHODS: Renal tissue was obtained from five patients who received nephrectomies. Each renal hydroxylation and glucuronidation enzymatic activities in microsomal fractions from patients were performed discretely and their estimation based on the decrease of propofol concentration. Hepatic hydroxylation and glucuronidation activities were also performed separately using human liver microsomes. This estimation is based on the decrease of propofol concentration, assuming that the contribution of hydroxylation activity without NADPH-generating system and glucuronidation activity without UDPGA in each microsomal fraction are negligible. Both renal and hepatic clearances were estimated assuming a well-stirred model. RESULTS: Enzymatic activity of propofol oxidation in renal microsomes was negligible. Although glucuronidation activity in microsomes from kidneys was comparable to that from liver, the hepatic intrinsic clearance predicted from in vitro study was higher than that in kidneys due to the larger tissue volume and higher protein concentration. However, glucuronidation clearance in kidney is relatively similar to that in liver because of blood flow limitation of clearance in both tissues. CONCLUSION: The high degree of hydroxylation activity in liver microsomes is consistent with the blood flow-limited hepatic clearance of propofol. Although the activity of propofol glucuronidation in liver is higher, glucuronidation in kidney may be a substantial contributor.

Aged↗
PubMed2006

Total body propofol clearance (TBPC) after living-donor liver transplantation (LDLT) surgery is decreased in patients with a long warm ischemic time.

Metabolic capacity after liver transplant surgery may be affected by the graft size and by hepatic injury during the surgery. This study was carried out to investigate the postoperative total body propofol clearance (TBPC) in living-donor liver transplantation (LDLT) patients and to investigate the major factors that contribute to decreased postoperative TBPC in LDLT patients. Fourteen patients scheduled for LDLT were included in this study. Propofol was administered at a rate of 2.0 mg.kg(-1).h(-1) as a sedative in the intensive care unit (ICU) setting. To calculate TBPC, propofol arterial blood concentration was measured by HPLC. Five variables were selected as factors affecting postoperative TBPC; bleeding volume (BLD), warm ischemic time (WIT), cold ischemic time (CIT), graft weight/standard liver volume ratio (GW/SLV), and portal blood flow after surgery (PBF). After factor analysis of six variables, including TBPC, varimax rotation was carried out, and this yielded three interpretable factors that accounted for 75.5% of the total variance in the data set. TBPC, WIT, CIT, and BLD were loaded on the first factor, PBF on the second factor, and GW/SLV on the third factor. The adjusted correlation coefficient between TBPC and WIT showed the highest value (r = -0.61) in the first factor. The LDLT patients were divided into two groups according to WIT; group A (WIT > 100 min) and group B (WIT < 100 min). Mean TBPC values in group A and group B were 14.6 +/- 2.1 and 28.5 +/- 4.1 ml.kg(-1).min(-1), respectively (P < 0.0001). These data suggest that LDLT patients with a long WIT have a risk of deteriorated drug metabolism.

Adolescent↗
PubMed2006

VKORC1 gene variations are the major contributors of variation in warfarin dose in Japanese patients.

OBJECTIVES: To compare the genetic and clinical factors that cause large interpatient variability and ethnic differences in warfarin efficacy, we investigated variations of the VKORC1, CYP2C9, and CYP2C19 genes in Japanese subjects. Furthermore, we evaluated the genetic variations and clinical data as contributors of variation in warfarin maintenance dose. METHODS: Gene variations of VKORC1, CYP2C9, and CYP2C19 in 125 patients treated with warfarin and 114 healthy subjects were analyzed. The daily dose of warfarin, concentrations of S- and R-warfarin in plasma, and prothrombin time expressed as the international normalized ratio were used as the pharmacokinetic and pharmacodynamic indices. Data were evaluated by a multivariate analysis method. RESULTS: Three missense mutations (47 G>C, 113 A>C, and 1338 A>G) in VKORC1 were newly identified in the Japanese population. The 113 A>C (Asp38Ser) variant decreased the warfarin dose requirement from 3.33 +/- 1.54 mg/d (n = 122) to 1.5 mg/d (n = 1). The variants -1639 G>A in the 5'-upstream region, 1173 C>T in intron 1, and 1542 G>C in intron 2 were in complete linkage disequilibrium, and the frequency of the -1639 G>A variation was only 0.8%, which contrasts with the frequency (39.8%-45.8%) reported previously for white persons. The dose of warfarin was larger in the VKORC1 -1639 GA genotype group (4.55 +/- 1.75 mg/d, P < .001) than in the -1639 AA group (2.94 +/- 1.15 mg/d). The mean daily dose of warfarin was lower in subjects with CYP2C9*1/*3 (1.86 +/- 0.80 mg/d, P = .007) than in subjects with CYP2C9*1/*1 (3.36 +/- 1.43 mg/d). When the relative contributions of the VKORC1 variants, CYP2C9*2, CYP2C9*3, CYP2C19*2, and CYP2C19*3, as well as the clinical characteristics of the patients, diagnoses, and concurrent medications, were compared, the VKORC1 -1639 GA genotype group accounted for 16.5% and CYP2C9 variants accounted for 13.4% of variation in warfarin dose. CONCLUSION: The ethnic difference in warfarin maintenance dose was mainly dependent on the linked VKORC1 variants. Genotyping of -1639 G>A of the VKORC1 gene could be clinically important for predicting individual variability in anticoagulant responses to warfarin.

Adult↗
PubMed2006

Influence of atropine on the dose requirements of propofol in humans.

OBJECTIVE: The purpose of this study was to evaluate the effect of atropine on the dose requirement of propofol for induction of anesthesia and propofol concentrations during continuous infusion. METHODS: Study 1: Forty patients were randomly allocated to the control or atropine groups. Induction of anesthesia commenced 3 min following the administration of 0.9% saline or atropine (0.01 mg kg(-1)), using a Diprifuser set to achieve propofol concentration of 6.0 microg mL(-1). The primary end point was the propofol dose per kg at the moment of loss of response to a command. Study 2: Fifteen patients undergoing elective surgery were enrolled. Propofol was administered to all subjects via target-controlled infusion to achieve a propofol concentration at 2.0 microg mL(-1) after intubation. Before and after administration of atropine (0.01 mg kg(-1)), cardiac output (CO) was measured using indocyanine green as an indicator and blood propofol concentration was determined using high-performance liquid chromatography. RESULTS: Study 1: The propofol dose for each group was 2.22+/-0.21 mg kg(-1) for control group and 2.45+/-0.28 mg kg(-1) for atropine, respectively (p=0.014). Study 2: After the administration of atropine, CO was significantly increased from 4.28+/-0.83 to 5.76+/-1.55 l min(-1) (p<0.0001). Propofol concentration was significantly decreased from 2.12+/-0.28 to 1.69+/-0.27 microg mL(-1) (p<0.0001). CONCLUSIONS: Following the administration of atropine, the propofol requirements for the induction of anesthesia were increased and propofol concentrations were decreased during continuous infusion by the administration of atropine.

Adult↗
PubMed2005

Genetic polymorphism of CYP2C9 and CYP2C19 in a Bolivian population: an investigative and comparative study.

OBJECTIVE: Several reports of CYP2C genetic polymorphism demonstrate its potential clinical role in determining both inter-individual and inter-ethnic differences in drug efficacy. We estimated the distribution of CYP2C9 and CYP2C19 common variants in the Bolivian population (a South American population), and compared these data with those from Asian, African, Caucasian and Oceanian populations. METHODS: Genomic DNA was obtained from 778 unrelated healthy volunteers from Bolivia. The genotypic status of CYP2C9 and CYP2C19 was determined by means of polymerase chain reaction-restriction fragment length polymorphism. RESULTS: Allelic and genotypic frequencies of CYP2C9 and CYP2C19 were determined for the Bolivian population, and comparison of the data with other ethnic groups revealed a lower CYP2C9*2 frequency (4.8%) than in Caucasians, but a higher frequency than in Asians; frequencies of CYP2C9*3 (3.0%) and CYP2C9 (0.4%) poor metabolizers (PMs) were similar to those seen in Asian populations. Frequencies of CYP2C19*2 (7.8%), CYP2C19*3 (0.1%), and CYP2C19 PMs (1.0%) in the Bolivian population were for the most part lower than in Caucasian, Asian, Oceanian and African populations. CONCLUSION: This is the first study to investigate a South American population for genetic polymorphism in the CYP2C subfamily. The Bolivian population differs from most other ethnic groups in the incidence of CYP2C9 and CYP2C19 common variants that might be influenced by its admixture characteristics.

Adolescent↗
PubMed2005

A dopamine infusion decreases propofol concentration during epidural blockade under general anesthesia.

PURPOSE: It is common clinical practice to use dopamine to manage the reduction in blood pressure accompanying epidural blockade. As propofol is a high-clearance drug, propofol concentrations can be influenced by cardiac output (CO). The purpose of the present study was to investigate the effects of dopamine infusions on propofol concentrations administered by a target-controlled infusion system during epidural block under general anesthesia. METHODS: 12 patients undergoing abdominal surgery were enrolled in this study. Anesthesia was induced with propofol and vecuronium 0.1 mg.kg(-1), and maintained using 67% nitrous oxide, sevoflurane in oxygen and constant infusion of propofol. Propofol was administered to all subjects via target-controlled infusion to achieve a propofol concentration at 6.0 microg.mL(-1) at intubation and 2.0 microg.mL(-1) after intubation. Before and after the administration of 10 mL of 1.5% mepivacaine from the epidural catheter and dopamine infusion at 5 microg.kg(-1).min(-1), CO and effective liver blood flow (LBF) were measured using indocyanine green. Blood propofol concentration was also determined using high-performance liquid chromatography. RESULTS: At one hour after epidural block and dopamine infusion, CO was significantly increased from 4.30 +/- 1.07 L.min(-1) to 5.82 +/- 0.98 L.min(-1) (P < 0.0001), and effective LBF was increased 0.75 +/- 0.17 L.min(-1) to 0.96 +/- 0.18 L.min(-1) (P < 0.0001). Propofol concentration was significantly decreased from 2.13 +/- 0.24 microg.mL(-1) to 1.59 +/- 0.29 microg.mL(-1) (P < 0.0001). CONCLUSIONS: Propofol concentrations decrease with an increase in CO, suggesting the possibility of inadequate anesthetic depth following catecholamine infusion during propofol anesthesia.

Aged↗
PubMed2005

Human kidneys play an important role in the elimination of propofol.

BACKGROUND: Extrahepatic clearance of propofol has been suggested because its total body clearance exceeds hepatic blood flow. However, it remains uncertain which organs are involved in the extrahepatic clearance of propofol. In vitro studies suggest that the kidneys contribute to the clearance of this drug. The purpose of this study was to confirm whether human kidneys participate in propofol disposition in vivo. METHODS: Ten patients scheduled to undergo nephrectomy were enrolled in this study. Renal blood flow was measured using para-aminohippurate. Anesthesia was induced with vecuronium (0.1 mg/kg) and propofol (2 mg/kg) and then maintained with nitrous oxide (60%), sevoflurane (1 approximately 2%) in oxygen, and an infusion of propofol (2 mg . kg . h). Radial arterial blood for propofol and para-aminohippurate analysis was collected from a cannula inserted in the radial artery. The renal venous sample and the radial arterial sample were obtained at the same time after the steady state of propofol was established. RESULTS: The renal extraction ratio of propofol was 0.58 +/- 0.15 (mean +/- SD). The renal clearance of propofol was 0.41 +/- 0.15 l/min (mean +/- SD), or 27 +/- 9.9% (mean +/- SD) of total body clearance. CONCLUSION: Human kidneys play an important role in the elimination of propofol.

Aged↗
PubMed2005

Kidneys contribute to the extrahepatic clearance of propofol in humans, but not lungs and brain.

AIMS: The principal site for the metabolism of propofol is the liver. However, the total body clearance of propofol is greater than the generally accepted hepatic blood flow. In this study, we determined the elimination of propofol in the liver, lungs, brain and kidneys by measuring the arterial-venous blood concentration at steady state in patients undergoing cardiac surgery. METHODS: After induction of anaesthesia, propofol was infused continuously during surgery. For measurement of propofol concentration, blood samples were collected from the radial and pulmonary artery at predetermined intervals. In addition, blood samples from hepatic and internal jugular vein were collected at the same times in 19 patients in whom a hepatic venous catheter was fitted and the other six in whom an internal jugular venous catheter was fitted, respectively. In six out of 19 patients fitted with a hepatic venous catheter, blood samples from the radial artery and the renal vein were also collected at the same time, when the catheter was inserted into the right renal vein before insertion into the hepatic vein. RESULTS: Hepatic clearance of propofol was approximately 60% of total body clearance. The hepatic extraction ratio of propofol was 0.87 +/- 0.09. There was no significant difference in the concentration of propofol between the radial, pulmonary arteries and internal jugular vein. However, a high level of propofol extraction in the kidneys was observed--the renal extraction ratio being 0.70 +/- 0.13. CONCLUSIONS: We have demonstrated substantial renal extraction of propofol in human. Metabolic clearance of propofol by the kidneys accounts for almost one-third of total body clearance and may be the major contributor to the extrahepatic elimination of this drug.

Adult↗
PubMed2005

Time-dependent induction of midazolam-1-hydroxylation enzymes in rats treated with St. John's wort.

Time-dependent effects of St. John's wort (SJW) on midazolam 1-hydroxylation were investigated in Wistar rats. Wistar rats treated with SJW (1000 mg/kg/d) for 1, 3, and 7 d were administered midazolam orally at a dose of 10 mg/kg. Oral clearance of midazolam in the SJW treated rats increased time dependently, and was significant after 7 d of treatment with SJW. The midazoram-1-hydroxylation activity in liver microsomes obtained from the SJW treated rats was significantly higher than in the control group. Linear correlation was observed between oral clearance and midazolam-1-hydroxylation activity in the liver microsomes, suggesting that CYP3A induction in liver mainly decreased the midazolam concentration in plasma. Immunoblotting revealed that the protein amount of CYP3A was induced within 3 d of SJW treatment. Since the midazolam-1-hydroxylation activity continuously increased for at least 7 d, the induction of CYP3A by SJW continued to cause interactions with drugs metabolized by CYP3A. It is important for persons receiving SJW for an extended time to consider its interactions with prescription drugs.

Animals↗
PubMed2005

Thiopurine methyltransferase genotype and phenotype status in Japanese patients with systemic lupus erythematosus.

We investigated the genotypic status of thiopurine methyltransferase (TPMT) polymorphism to evaluate the possible risk of the toxicity of azathioprine (AZA) in 68 patients with systemic lupus erythematosus (SLE). The allele frequency of TPMT mutation in the SLE group (2.9%) was higher than that in 174 Japanese healthy volunteers (1.1%), although it did not reach statistically significant difference (p=0.23). The mean value of TPMT activities in 51 subjects with TPMT*1/*1 was 40% higher than that of 4 subjects with TPMT*1/*3C in SLE group (18.1+/-6.1 nmol/h/ml packed red blood cells (pRBC) versus 13.2+/-3.2 nmol/h/ml pRBC; p=0.11). Two out of 4 SLE patients with TPMT*1/*3C had been treated with AZA, and one patient showed a leucopenia. The TPMT genotyping before AZA treatment is recommended for Japanese SLE patient group to avoid the AZA-induced adverse events, although detection of the patient with low TPMT activity by genotyping is still imperfect.

Adolescent↗
PubMed2005

Genotyping of thiopurine methyltransferase using pyrosequencing.

Thiopurine methyltransferase (TPMT) metabolizes thiopurine drugs which are used in the treatment of leukemia and some autoimmune diseases. Previously, 11 mutant alleles of TPMT gene (TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8) have been reported. These mutant alleles may cause life-threatening toxicity in patients exposed to thiopurine drugs, 6-mercaptopurine and azathioprine. We have developed a rapid and accurate protocol for TPMT genotype determination using Pyrosequencing(TM) technology in 96 Japanese subjects. Five fragments of the TPMT gene (exon 4, 5, 7, 8, 10) were amplified by PCR, and the 10 single-nucleotide polymorphisms (SNPs) for TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8 were sequenced. The results of this pyrosequencing method corresponded exactly with those of the DNA sequencing method using BigDye terminator chemistry. We have demonstrated that typing of 10 SNPs can be performed within 30 min. Pyrosequencing has a wide application in the large-scale identification of individual TPMT genotypes.

Adult↗
PubMed2005

Inhibitory effects of nicardipine to cytochrome P450 (CYP) in human liver microsomes.

To anticipate drug-drug interactions by nicardipine in vivo, cytochrome P450 (CYP) forms responsible for the metabolism of nicardipine and inhibition of CYP-dependent drug metabolism by nicardipine were investigated. Microsomes of human B-lymphoblastoid cells expressing each human CYP form were used for the metabolism of nicardipine. Inhibitory effects of nicardipine on drug metabolism were studied using human liver microsomes. CYP2C8, CYP2D6 and CYP3A4 were identified as major CYP forms for the metabolism of nicardipine in human liver microsomes. Nicardipine strongly inhibited two-pathways of triazolam hydroxylation both catalyzed by CYP3A4. Comparison of three Ca(2+) antagonists, nicardipine, nifedipine, and diltiazem revealed that only nicardipine showed such a strong inhibitory potency on the typical CYP2D6-catalyzed drug metabolism. Furthermore, nicardipine inhibited other reactions catalyzed by CYP1A, CYP2A6, CYP2C8, CYP2C9 and CYP2C19 with K(i) values ranging from 1.1 to 29.4 microM. In conclusion, nicardipine was a relatively potent inhibitor of human CYP2D6, CYP3A4 and CYP2C (especially for CYP2C8 and CYP2C19) in vitro, suggesting that drug-drug interactions between nicardipine and other drugs metabolized mainly by these CYP forms appear to occur in vivo.

Cell Line↗
PubMed2004

Changes in drug plasma concentrations of an extensively bound and highly extracted drug, propofol, in response to altered plasma binding.

OBJECTIVE: Cardiopulmonary bypass is known to result in a reduction in the plasma binding of drugs. The resulting effect on the hepatic clearance of drugs with low extraction is well understood. However, the situation with those that are highly extracted is less clear. Studies were, therefore, undertaken with one such drug, propofol, for which plasma binding was changed during cardiac surgery with cardiopulmonary bypass. METHODS: After induction of anesthesia with midazolam in 19 patients, propofol was infused continuously at a rate of 4 mg. kg(-1). h(-1) during surgery. Propofol's concentration was measured by HPLC in blood samples collected from the radial artery and hepatic vein during surgery at predetermined intervals. The drug's unbound fraction in arterial plasma was estimated via equilibrium dialysis. RESULTS: The total concentration of propofol in blood was unchanged during surgery except shortly after the initiation of cardiopulmonary bypass. By contrast, the fraction of unbound propofol in blood increased by 2-fold during cardiopulmonary bypass and then decreased after the completion of cardiopulmonary bypass. The hepatic extraction ratio of propofol was greater than 0.8 and remained constant throughout surgery. The ratio of propofol concentration in erythrocytes to that in blood increased by 1.6-fold during cardiopulmonary bypass. CONCLUSIONS: During cardiopulmonary bypass, a significant increase in the concentration of unbound propofol occurred without alteration in the total propofol concentration in blood. The effect of the changes of propofol's protein binding on its kinetics was consistent with the predictions based on the well-stirred model of hepatic elimination for an intravenously infused high-clearance drug. Our finding on propofol pharmacokinetics may be the first example demonstrating the theoretic prediction of the well-stirred model.

Adult↗
PubMed2004

Unstable plasma thalidomide concentration in patients with refractory multiple myeloma.

In this study, we analyzed the relationship between the plasma concentration of thalidomide and the therapeutic effect obtained by using thalidomide alone in patients with refractory multiple myeloma. The safety and effect of thalidomide was examined in 12 cases of refractory multiple myeloma. Four cases (33%) achieved partial response (PR) and 3 cases (25%) achieved minimal response. These effects were achieved with only 200 mg/day of thalidomide and maintained with 100-200 mg/day. The concentration of thalidomide in the blood was measured in 7 cases; dose-dependency was not recognized. In 5 cases in which complete or partial response was obtained, the effect was obtained with a mean thalidomide concentration in blood of 0.5 microg/mL or less. However, in 2 cases in which the mean blood concentration of thalidomide was 2 microg/mL or higher, an M-protein-reducing effect was not obtained. The frequency of various side effects was increased when the concentration of thalidomide was higher than 2 microg/mL. In conclusion, low-dose thalidomide therapy may effectively treat refractory myeloma, and the measurement of thalidomide concentration in the blood may not be a marker of therapeutic effect, but rather a marker of adverse effects.

Aged↗