Biomedical subjects

L S Chen

Publications and source records attributed to L S Chen.

At least 55 records · Page 3Linked to original sources

PubMed1996

Effect of octreotide on total effective vascular compliance in patients with posthepatitic cirrhosis.

BACKGROUND/AIMS: This study aimed to evaluate the effect of octreotide on total effective vascular compliance, measured during rapid volume expansion, in patients with posthepatitic cirrhosis. METHODS: Twenty-nine patients with posthepatitic cirrhosis were randomly assigned to receive a 100-micrograms/h infusion of octreotide after a 100-micrograms bolus (n = 15), or a placebo (n = 14). Hemodynamic measurements were recorded before and 30 min after drug administration. Thereafter, rapid volume expansion was performed in each patient and hemodynamic measurements were repeated immediately after volume expansion. RESULTS: Before volume expansion, placebo administration did not affect any of the hemodynamic values, while the hepatic blood flow was significantly decreased following octreotide administration. After volume expansion, the hemodynamic changes were similar between patients receiving octreotide and the placebo. However, the increase in right atrial pressure from the beginning to the end of volume expansion was higher and the total effective vascular compliance was lower in patients receiving octreotide (+3.5 +/- 0.3 mmHg, p = 0.05 and 1.69 +/- 0.16 ml.mmHg-1.kg-1, p < 0.05) compared to patients receiving placebo (+2.5 +/- 0.3 mmHg, 2.60 +/- 0.34 ml.mmHg-1.kg-1). CONCLUSIONS: The present study suggests that octreotide decreased total effective vascular compliance in patients with posthepatitic cirrhosis. It is possible that, in patients with posthepatitic cirrhosis, venoconstriction was induced following octreotide administration.

Aged↗

PubMed1996

Prevalence of gastric ulcer in cirrhotic patients and its relation to portal hypertension.

The prevalence of gastric ulcer and its relationship to the severity of cirrhosis and degree of portal hypertension was evaluated in 245 cirrhotic patients, and compared with 245 age- and sex-matched healthy subjects. Portal and systemic haemodynamic studies were performed in cirrhotic patients. The prevalence of gastric ulcer in cirrhotic patients was 20.8%, which was significantly higher than the 4.0% found in healthy controls. Using a multivariate logistic regression model, the hepatic venous pressure gradient was found to be the only predictor of the prevalence of gastric ulcer in cirrhotic patients to present with gastric ulcer. The hepatic venous pressure gradient was significantly higher in cirrhotic patients with gastric ulcer than in those without (17.3 +/- 4.4 vs 15.5 +/- 5.0 mmHg, P = 0.01). Other variables, including sex, smoking, cardiac output and severity or aetiology of cirrhosis did not show significant differences between the two patient groups. The prevalence of gastric ulcer in cirrhotic patients whose hepatic venous pressure gradient was below 12 mmHg (4.5%) was similar to that observed in the healthy controls (4.0%). However, when the hepatic venous pressure gradient was > 12 mmHg, the prevalence of gastric ulcer (24.4%) was significantly higher than that in control subjects. However, the incidence of gastric ulcer was not related to the degree of portal hypertension. In conclusion, the prevalence of gastric ulcer in cirrhotic patients was found to be significantly higher than in the age- and sex-matched healthy subjects. Portal hypertension with a hepatic venous pressure gradient > 12 mmHg may be an important factor contributing to the increased prevalence of gastric ulcer observed in patients with liver cirrhosis.

Case-Control Studies↗

PubMed1996

Plasma interleukin-8 levels in patients with post-hepatitic cirrhosis: relationship to severity of liver disease, portal hypertension and hyperdynamic circulation.

The present study investigated plasma levels of interleukin-8 (IL-8) in patients with post-hepatitic cirrhosis and correlated it with the severity of liver diseases and haemodynamic parameters. Plasma IL-8 levels were significantly higher in 57 post-hepatitic cirrhotic patients (7.5 +/- 1.8 pg/mL; P < 0.005) than those in 41 healthy subjects (2.0 +/- 0.2 pg/mL). Elevated (> 5 pg/mL) plasma IL-8 levels were found in up to 30% of cirrhotic patients. In cirrhotic patients, plasma IL-8 levels progressively increased in relation to the severity of liver dysfunction (4.5 +/- 1.0, 4.9 +/- 1.4 and 20.5 +/- 8.3 pg/mL for Pugh's class A, B and C, respectively; P < 0.005). A significant correlation was observed between plasma IL-8 levels and serum bilirubin levels (r = 0.72; P < 0.001). There were no differences in the hepatic venous pressure gradient (15.4 +/- 1.1 vs 15.1 +/- 0.9 mmHg; P > 0.05) and systemic vascular resistance (1119 +/- 118 vs 1199 +/- 54 dyn.s/cm5; P > 0.05) between cirrhotic patients with and without elevated plasma IL-8 levels. In addition, plasma IL-8 levels did not correlate with hepatic venous pressure gradient (r = 0.26; P > 0.05) and systemic vascular resistance (r = -0.24; P > 0.05). These results demonstrate that plasma IL-8 levels are increased in patients with post-hepatitic cirrhosis. The severity of liver cirrhosis is an important factor for the occurrence of enhanced IL-8 levels. IL-8 does not play a role in the hyperdynamic circulation observed in patients with post-hepatitic cirrhosis.

Bilirubin↗

PubMed1996

Portal hypertensive colopathy in patients with cirrhosis.

BACKGROUND: Colonic vascular ectasias and colorectal varices have been observed in patients with cirrhosis. However, the pathogenesis of these vascular lesions has not been established. METHODS: We enrolled 35 cirrhotic patients and 20 normal controls in this study. All received colonoscopic examinations and measurements of plasma glucagon levels. Portal pressure measurements were performed in all the cirrhotic patients. RESULTS: Colonic vascular ectasias occurred more commonly in cirrhotic patients than in controls (17 of 35 versus 0 of 20; p = 0.009) and more commonly in cirrhotic patients with ascites than in those without (15 of 24 versus 2 of 11; p = 0.038). However, the presence of colonic vascular ectasias was not related to the hepatic venous pressure gradient or plasma glucagon levels. Colorectal varices also occurred more commonly in cirrhotic patients than in controls (16 of 35 versus of 1 of 20; p = 0.034), but the hepatic venous pressure gradient, plasma glucagon levels, and severity of cirrhosis were not related to the presence of colorectal varices. CONCLUSIONS: Portal hypertension per se and increased plasma glucagon levels may not play an important role in the pathogenesis of colonic vascular ectasias or colorectal varices in patients with cirrhosis.

Aged↗

PubMed1996

The murine amelogenin promoter: developmentally regulated expression in transgenic animals.

We are interested in understanding hierarchical regulation pathways that control gene expression in developing teeth. In pursuit of the molecular basis for the regulated expression of amelogenin by developing ameloblasts during tooth formation, we isolated the murine amelogenin promoter. Analysis of this promoter will provide additional details towards the identification of signals generated through instructive-, dissimilar-germ layer interactions that are for responsible for temporal- and spatial-regulation for amelogenin gene expression. Using transgenic mice we demonstrate that a 2263 nucleotide stretch of the murine amelogenin promoter conveys appropriate temporal- and spatial-regulation for amelogenin gene expression in response to instructive-signals. These transgenic animals are useful reagents to further dissect signaling pathways responsible for regulated gene expression by terminally differentiated ameloblasts.

3T3 Cells↗

PubMed1996

Widespread neuronal expression of the presenilin-1 early-onset Alzheimer's disease gene in the murine brain.

Mutations in the presenilin-1 (S182) gene have been genetically linked to early-onset Alzheimer's disease. To clarify the underlying molecular mechanism through which presenilin-1 is involved in the pathogenesis of this neurodegenerative disorder, the regional and cellular transcription profile of this gene was characterized in primary cells isolated from the murine brain by Northern blot hybridization using digoxigenin-labeled riboprobes. Our results indicate that presenilin-1 mRNA transcripts are widely distributed throughout the adult mouse brain. Furthermore, immunohistochemical labeling of hybridized sections indicates that expression was predominantly localized to neuronal cells. Neurons in the hippocampus and cerebral cortex, which are severely compromised in Alzheimer's disease, showed prominent expression of presenilin-1. In contrast, white matter areas and endothelial cells do not appear to express presenilin-1 to detectable levels. presenilin-1 transcripts, however, are also present less frequently in certain nonneuronal cell populations such as ependymal cells in the choroid plexus. Analysis of primary cells isolated from murine brain supported the results obtained by in situ hybridization and showed that cultured primary neurons and astrocytes express presenilin-1. Overall, it appears that the pattern of presenilin-1 gene expression parallels that previously described for the amyloid precursor protein.

Alzheimer Disease↗

PubMed1995

Long QT syndrome patients with mutations of the SCN5A and HERG genes have differential responses to Na+ channel blockade and to increases in heart rate. Implications for gene-specific therapy.

BACKGROUND: The genes for the long QT syndrome (LQTS) linked to chromosomes 3 (LQT3) and 7 (LQT2) were identified as SCN5A, the cardiac Na+ channel gene, and as HERG, a K+ channel gene. These findings opened the possibility of attempting gene-specific control of ventricular repolarization. We tested the hypothesis that the QT interval would shorten more in LQT3 than in LQT2 patients in response to mexiletine and also in response to increases in heart rate. METHODS AND RESULTS: Fifteen LQTS patients were studied. Six LQT3 and 7 LQT2 patients were treated with mexiletine, and its effects on QT and QTc were measured. Mexiletine significantly shortened the QT interval among LQT3 patients (QTc from 535 +/- 32 to 445 +/- 31 ms, P < .005) but not among LQT2 patients (QTc from 530 +/- 79 to 503 +/- 60 ms, P = NS). LQT3 patients (n = 7) shortened their QT interval in response to increases in heart rate much more than LQT2 patients (n = 4) and also more than 18 healthy control subjects (9.45 +/- 3.3 versus 3.95 +/- 1.97 and 2.83 +/- 1.33, P < .05; data expressed as percent reduction in QT per 100-ms shortening in RR). Among these patients, there is also a trend for LQT2 patients to have syncope or cardiac arrest under emotional or physical stress and for LQT3 patients to have cardiac events either at rest or during sleep. CONCLUSIONS: This is the first study to demonstrate differential responses of LQTS patients to interventions targeted to their specific genetic defect. These findings also suggest that LQT3 patients may be more likely to benefit from Na+ channel blockers and from cardiac pacing because they would be at higher risk of arrhythmia at slow heart rates. Conversely, LQT2 patients may be at higher risk to develop syncope under stressful conditions because of the combined arrhythmogenic effect of catecholamines with the insufficient adaptation of their QT interval when heart rate increases.

Adult↗

PubMed1995

Comparison of metabolic fluxes of cis-5-enoyl-CoA and saturated acyl-CoA through the beta-oxidation pathway.

The metabolic fluxes of cis-5-enoyl-CoAs through the beta-oxidation cycle were studied in solubilized rat liver mitochondrial samples and compared with saturated acyl-CoAs of equal chain length. These studies were accomplished using either spectrophotometric assay of enzyme activities and/or the analysis of metabolites and precursors using a gas chromatographic method after conversion of CoA esters into their free acids. Cis-5-enoyl-CoAs were dehydrogenated by acyl-CoA oxidase or acyl-CoA dehydrogenases at significantly lower rates (10-44%) than saturated acyl-CoAs. However, enoyl-CoA hydratase hydrated trans-2-cis-5-enoyl-CoA at a faster rate (at least 1.5-fold) than trans-2-enoyl-CoA. The combined activities of 3-hydroxyacyl-CoA dehydrogenase and 3-ketoacyl-CoA thiolase for 3-hydroxy-cis-5-enoyl-CoAs derived from cis-5-enoyl-CoAs were less than 40% of the activity for the corresponding 3-hydroxyacyl-CoAs prepared from saturated acyl-CoAs. Rat liver mitochondrial beta-oxidation enzymes were capable of metabolizing cis-5-enoyl-CoA via one cycle of beta-oxidation to cis-3-enoyl-CoA with two less carbons. However, the overall rates of one cycle of beta-oxidation, as determined with stable-isotope-labelled tracer, was only 15-25%, for cis-5-enoyl-CoA, of that for saturated acyl-CoA. In the presence of NADPH, the metabolism of cis-5-enoyl-CoAs was switched to the reduction pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1995

Isomerization of trans-2,delta 5-dienoyl-CoA's to delta 3,delta 5-dienoyl-CoA's in the beta-oxidation of delta 5-unsaturated fatty acids.

The NADPH-dependent reduction pathway for the metabolism of delta 5-unsaturated fatty acids involves the isomerization of trans-2,delta 5-dienoyl-CoA, initially formed from the dehydrogenation of delta 5-enoyl-CoA, to isomeric delta 3,delta 5-dienoyl-CoA. The latter intermediates were then isomerized to trans-2,trans-4-dienoyl-CoA, which then follows the NADPH-dependent pathway mediated by 2,4-dienoyl-CoA reductase. The isomerization from trans-2,delta 5-dienoyl-CoA to delta 3,delta 5-dienoyl-CoA is catalyzed by delta 3,delta 2-enoyl-CoA isomerase. In this investigation, we identified the stereoisomers of delta 3,delta 5-dienoates that were formed in the reaction. Starting from trans-2,cis-5-decadienoyl-CoA, the isomerization produced cis-3,cis-5- and trans-3,cis-5-decadienoates. On the other hand, trans-2,trans-5-decadienoyl-CoA yielded cis-3,trans-5- and trans-3,trans-5-decadienoates. In addition to purified rat liver delta 3,delta 2-enoyl-CoA isomerase, acyl-CoA oxidase from Arthrobacter also catalyzed the isomerization from trans-2,cis-5-dienoyl-CoA. However, this acyl-CoA oxidase could not catalyze the similar isomerization of trans-2,trans-5-dienoyl-CoA. delta 3,delta 5-t-2,t-4-Dienoyl-CoA isomerase used cis-3,cis-5-, trans-3,cis-5-, and cis-3,trans-5-dienoyl-CoA's as substrates and converted them to trans-2,trans-4-dienoyl-CoA. In contrast, trans-3,trans-5-dienoyl-CoA was not a substrate for this isomerization. Extensive purification of acyl-CoA oxidase through column chromatography could not remove or diminish the isomerization activity associated with acyl-CoA oxidase. Acyl-CoA oxidases derived from Candida and rat liver also possess isomerization activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl Coenzyme A↗

PubMed1995

Plasma endothelin levels in patients with cirrhosis and their relationships to the severity of cirrhosis and renal function.

BACKGROUND/AIMS: Increased plasma endothelin levels have been reported in patients with cirrhosis. However, the relationship between plasma endothelin concentrations and hyperdynamic circulation or renal functions has not been documented. METHODS: We measured the plasma endothelin-1 and endothelin-3 concentrations using radioimmunoassay in 96 patients with cirrhosis (Pugh's A in 26, Pugh's B in 45 and Pugh's C in 25) and compared these values to 56 age- and sex-matched healthy subjects. Systemic and portal hemodynamic measurements, effective renal plasma flow, creatinine clearance, plasma aldosterone concentration and plasma renin activity were recorded for each patient. RESULTS: Plasma endothelin-1 and endothelin-3 levels were significantly increased in patients with cirrhosis compared to healthy subjects. Additionally, plasma endothelin-1 and endothelin-3 values were higher in patients with cirrhosis and ascites than in those without ascites. Moreover, plasma endothelin-1 levels increased in relation to the severity of cirrhosis. On the other hand, modest negative correlations were found between endothelin-1 and creatinine clearance or effective renal plasma flow. CONCLUSIONS: Plasma endothelin-1 and endothelin-3 levels are increased in patients with cirrhosis compared to healthy subjects. The increase in plasma endothelin-1 levels is related at least in part to the severity of cirrhosis. Increased endothelin-1 levels may possibly contribute to renal dysfunction in patients with cirrhosis.

Adult↗

PubMed1995

Clinical utility of video-EEG monitoring.

This study investigated the efficiency of simultaneous video-electroencephalography (EEG) monitoring in documenting paroxysmal events, the value in clinical diagnosis, and the effect on treatment. In this retrospective review, 230 children underwent this procedure between January, 1990 and December, 1992. The data demonstrated that video-EEG monitoring can be used as a daytime procedure with a high success rate (80%) in detecting and differentiating the nature of recurrent paroxysmal behaviors that have occurred on a daily basis. Video-EEG monitoring has a high diagnostic rate in differentiating seizure versus nonseizure events (70%), in classifying seizure types (88%), and in evaluating the candidacy for epilepsy surgery (64%). Video-EEG diagnosis resulted in an alteration of clinical management in 45% of patients. Continuous video-EEG monitoring is an efficient and valuable procedure in the diagnosis and management of paroxysmal disorders in children.

Anticonvulsants↗

PubMed1995

Temperature sensitive simian virus 40 large T antigen immortalization of murine odontoblast cell cultures: establishment of clonal odontoblast cell line.

During tooth formation instructive epithelial-mesenchymal interactions result in the cytodifferentiation of ectomesenchymal cells into odontoblasts which produce the dentin extracellular matrix (DECM). The purpose of our study was to establish a stable murine odontoblast cell line by immortalization of odontoblasts using retrovirus transfection. In order to accomplish this goal, we utilized a previously characterized odontoblast monolayer cell culture system supportive of odontoblast cytodifferentiation from dental papilla mesenchyme (DPM), expression and secretion of a DECM and dentin biomineralization. First mandibular molars from E-18 Swiss Webster mice were dissected, the DPM isolated, and pulp cells dissociated. Pulp cells (5 x 10(5)/well) were plated as monolayers and grown in alpha-MEM supplemented with 10% FCS, 100 units/ml penicillin and streptomycin, 50 micrograms/ml ascorbic acid. Cultures were maintained for 6 days at 37 degrees C in a humidified atmosphere of 95% air and 5% CO2, with media changes every two days. Immortalization was performed using a recombinant defective retrovirus containing the temperature sensitive SV-40 large T antigen cDNA and the neomycin (G418) resistance gene recovered from CRE packaging cells. Cultures were infected for 24 h with CRE conditioned medium containing 8 micrograms/ml of polybrene, the media was replaced with selective media containing 300 micrograms/ml of G418, and the cultures incubated at 33 degrees C for one month with media changes every 3-5 days. Neomycin resistant cells were cloned by serial dilution to single cells in 96-well culture plates and grown in selection medium at 33 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

[Aging changes of the electro-physiological characteristics of hypothalamic neurons in culture].

The aging changes of the electrophysiological characteristics of the hypothalamic neurons cultured for 0-140 days were studied in neonatal SD rats by the intracellular microelectrode recording technique. The growth velocity of the neurites was used as an index to divide the living process of the neurons into three periods, i.e. recovering period, growth period and aging period. It was found that the time constant and the membrane capacitance reached a top value in the growth period and then decreased significantly in the aging period (P < 0.05, P < 0.01). In the recovering period, the membrane resistance reached the highest; and then decreased significantly in growth period but did not change significantly in the aging period. The amplitude of the membrane resting potential was about -30 - -60 mv and increased with the days in vitro (P < 0.05). The neurons could produce single or burst discharges. It appears that certain electrophysiological characteristics of the hypothalamic neurons in culture could characterize certain aging changes.

Animals↗

PubMed1995

Prevalence of duodenal ulcer in cirrhotic patients and its relation to Helicobacter pylori and portal hypertension.

BACKGROUND: The prevalence of duodenal ulcer increases in cirrhotic patients. However, the pathogenesis remains unclear. METHODS: The prevalence of duodenal ulcer and their relationship to cirrhosis and portal hypertension were evaluated in 325 cirrhotic patients, and compared with 325 age- and sex-matched healthy subjects. Portal and systemic hemodynamic studies were performed in all cirrhotic patients. Histological examination of gastric antral mucosa for Helicobacter pylori (H. pylori) was performed in 16 cirrhotic patients with duodenal ulcer and in 34 cirrhotic patients without duodenal lesions. RESULTS: The prevalence of duodenal ulcer in cirrhotic patients was 9.5% (31 out of 325), significantly higher than 4.0% (13 out of 325) in the healthy controls (p = 0.007), but was not related to the severity of liver cirrhosis. The positive rate of H. pylori was not different between cirrhotic patients with duodenal ulcer and those without duodenal lesions (9/16 vs. 18/34, p > 0.05). The hepatic venous pressure gradient was also not different between these groups (17.2 +/- 5.1 vs. 16.1 +/- 4.9 mmHg, p > 0.05). Other variables including sex, smoking, and etiology of cirrhosis did not show significant differences. CONCLUSIONS: The prevalence of duodenal ulcer is significantly higher in cirrhotic patients than in the age- and sex-matched healthy subjects. The severity of cirrhosis, the presence of H. pylori or portal hypertension per se does not play an important role in the increased prevalence of duodenal ulcer in cirrhotic patients.

Duodenal Ulcer↗

PubMed1994

Stepwise immortalization and transformation of adult human prostate epithelial cells by a combination of HPV-18 and v-Ki-ras.

Recent investigations have shown the presence of ras gene mutations and human papillomavirus (HPV) DNA in prostate carcinomas. In the present study, secondary adult human prostatic epithelial cells, upon transfection with a plasmid containing the entire HPV-18 genome, acquired an indefinite life-span in culture but did not undergo malignant conversion. Subsequent infection of these immortalized cells with the Kirsten murine sarcoma virus, which contains an activated Ki-ras oncogene, induced morphological transformation that led to the acquisition of neoplastic properties. These findings demonstrate the malignant transformation of adult human prostate epithelial cells in culture by a combination of viral oncogenes and the successive roles of HPV infection and Ki-ras activation in a multistep process responsible for prostate carcinogenesis.

Adult↗

PubMed1994

Purification and mechanism of delta 3,delta 5-t-2,t-4-dienoyl-CoA isomerase from rat liver.

A new enzyme, i.e., delta 3,delta 5-t-2,t-4-dienoyl-CoA isomerase, required in the NADPH-dependent metabolic pathway of odd-numbered double bond, unsaturated fatty acids, was isolated and purified to apparent homogeneity from rat liver. In the oxidation of odd-numbered double bond, unsaturated fatty acids, stepwise beta-oxidation leads to cis-5-enoyl-CoA, which is then dehydrogenated and isomerized to delta 3,delta 5-dienoyl-CoA. delta 3,delta 5-t-2,t-4-Dienoyl-CoA isomerase converts delta 3,delta 5-dienoyl-CoA to trans-2,trans-4-dienoyl-CoA, which is a substrate for NADPH-dependent 2,4-dienoyl-CoA reductase. This enzyme was purified through Matrex gel red A, blue Sepharose, DEAE-cellulose, CM-cellulose, hydroxylapatite, and Sepharose CL6B column chromatography of an ammonium sulfate precipitated fraction (30-80%) of rat liver homogenate. A native molecular weight of 200,000 with four subunits of 55,000 each was determined. The isoelectric point was 6.5. This enzyme was located in mitochondria and was inducible by clofibrate treatment. Using delta 3,delta 5-decadienoyl-CoA, delta 3,delta 5-dodecadienoyl-CoA, and delta 3,delta 5-tetradecadienoyl-CoA as substrates, the Vmax ratio was 1:0.5:0.4 and the Km's were 10.9, 5.9, and 1.4 microM, respectively. The specific activity of purified enzyme was 7 units/mg using delta 3,delta 5-decadienoyl-CoA as substrate. The mechanism of isomerization was studied by deuterium labeling. Consistent with the deuterium labeling pattern of the products, the isomerization from trans-2,cis-5-dienoyl-CoA to trans-2,trans-4-dienoyl-CoA was a two-step process through an intermediate delta 3,delta 5-dienoyl-CoA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Hepatic microsomal tolbutamide hydroxylation in Japanese: in vitro evidence for rapid and slow metabolizers.

Microsomal hydroxylation of tolbutamide in Japanese livers was studied in vitro to ascertain the enzyme catalysing this reaction. Rates of tolbutamide hydroxylation differed individually 33-fold and 42-fold at 0.1 mM and 2.4 mM tolbutamide concentrations, respectively, and were segregated into two groups, rapid and slow metabolizers. An antibody raised against P450 human-2 (a form of CYP2C9) strongly inhibited the hydroxylation in livers of rapid metabolizers but only weakly inhibited in the slow metabolizer. Kinetic experiments further demonstrated a clear distinction in tolbutamide hydroxylation between two groups; the mean of apparent Km values for tolbutamide was 0.25 mM (n = 3) in the rapid group and 2.58 mM (n = 2) in the slow, respectively. These data suggest that different enzymes are involved in the hydroxylation in both metabolizer groups. Furthermore, CYP2C9 produced by cDNA expression in yeasts, catalysed tolbutamide hydroxylation at rates similar to the rapid metabolizer group at both the 0.1 mM and 2.4 mM concentrations. The apparent Km value of the expressed protein for tolbutamide, 0.26 mM, was similar to that determined for the rapid group of microsomal samples. Clear correlations were observed between the rate of microsomal tolbutamide hydroxylation at 0.1 mM and CYP2C9 protein content or the rate of S-mephenytoin 4'-hydroxylation in human liver. These results indicate that considerable portions of microsomal tolbutamide hydroxylation are catalysed by CYP2C9 or the closely related form in the rapid metabolizers.

Antibodies↗

PubMed1993

Cytochrome P450 mediated metabolism of diazepam in human and rat: involvement of human CYP2C in N-demethylation in the substrate concentration-dependent manner.

Metabolism of diazepam (DZP) was studied in vitro to clarify the involvement of different forms of hepatic cytochrome P450 (CYP) in rats, and humans of Japanese and Caucasian origin. Microsomal 3-hydroxylation was the major pathway of DZP metabolism in rats and was inhibited by anti-CYP3A antibodies. Purified CYP3As and CYP2C11 catalysed 3-hydroxylation and N-demethylation, respectively, in the reconstituted systems. The rates of both reactions in human liver microsomes depended on the substrate concentration: the rate of 3-hydroxylation was 3-4 times higher than N-demethylation at 0.2 mM; the two activities were essentially the same at a lower substrate concentration (0.02 mM). Inhibitions of the N-demethylation by anti-CYP2C antibody and S-mephenytoin also depended on the substrate concentration and was detectable only at a low substrate concentration. Kinetic studies revealed the presence of two distinct catalytic activities for the N-demethylation; low Km and low Vmax, and high Km and high Vmax. The former activity seems to be mediated by a CYP2C P450 form. On the other hand, DZP 3-hydroxylation was rather selectively catalysed by a CYP3A P450 at the low and high substrate concentrations. These results were consistent with the observation in vivo that DZP N-demethylation and S-mephenytoin 4'-hydroxylation are closely correlated in humans. These results also suggest that the apparent discrepancy on the role of CYP forms in DZP metabolism in vitro and in vivo may reside in the difference in substrate concentration.

Adolescent↗