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M L Chen

Publications and source records attributed to M L Chen.

At least 181 records · Page 10Linked to original sources
PubMed1986

Characteristics of pre-S2 region of hepatitis B virus.

The nucleotide sequence of our cloned HBV DNA (subtype adw) has been determined. When the 165-nucleotide sequence of the pre-S2 region was compared with 7 other published sequences (subtypes adw, adr, ayw, and adyw), we found 38 nucleotide substitutions among different subtypes and 4 (adr) or 6 (adw and ayw) substitutions within the same subtype. Analysis of the predicted amino acid sequence from the known nucleotide sequences indicates that: there are 20 amino acid substitutions, the longest conserved amino acid sequence is located between amino acids 23 to 34, and the 54th amino acid is identical within the same subtype but varies in different subtypes.

Amino Acid Sequence↗
PubMed1984

Simple and micro high-performance liquid chromatographic method for simultaneous determination of p-aminohippuric acid and iothalamate in biological fluids.

A simple, rapid and micro high-performance liquid chromatographic method was developed for separate or simultaneous determination of p-aminohippuric acid and iothalamate in plasma and urine using p-aminobenzoic acid as an internal standard. The method involved deproteinizing samples with two volumes of acetonitrile followed by injection of 5 microliters of deproteinized supernatant onto a C18 reversed-phase column. The mobile phase contained 3.5% acetonitrile in 0.04% phosphoric acid and flowed at a rate of 1.5 ml/min. The column effluent was monitored by an ultraviolet detector at 254 nm. Retention times for p-aminohippuric acid, iothalamate and p-aminobenzoic acid were approximately 4.5, 6 and 8 min, respectively. This method requires as little as 5 microliters of sample and can be used to measure accurately down to 1 microgram/ml p-aminohippuric acid and 0.5 microgram/ml iothalamate in plasma samples. The coefficients of variation of the assay with or without the use of internal standard were generally low (below 7%). No interferences from endogenous substances or any drugs tested were found.

4-Aminobenzoic Acid↗
PubMed1984

Effect of dietary vegetable (water convolvulus) on cholesterol metabolism in rats.

Male rats were fed diets containing 0.5% cholesterol with or without vegetable (water convolvulus) or neutral detergent fiber supplementation. After 2 weeks, rats were given [4-14C]cholesterol i.p. Feces were collected for 1 week. Three hours prior to necropsy, [3H]acetate was administered i.p. Samples of serum, liver, adipose tissue, muscle and brain were obtained for analysis. Concentrations of total lipids and cholesterol and synthesis and recovery of labeled steroids are reported. Results showed that the growth of animals and food utilization were not significantly affected by different dietary treatments. The notable effect of vegetable was that the elevated liver and serum cholesterol levels due to increased intake can be nearly offset by increasing the fecal excretion. The high rate of excretion of 14C-labeled steroids shown in vegetable-fed rats indicated that both decreased absorption and increased endogenous excretion occurred in these animals. The synthesis of total lipids as demonstrated by [3H]acetate incorporation was not affected appreciably by diet. In liver, however, cholesterol synthesis appeared to be lower in rats receiving cholesterol-supplemented diet, but higher in rats fed vegetable diets. The ratio of 3H:14C of liver cholesterol was significantly higher in rats fed the vegetable diet. In brain cholesterol we also found consistently high 3H:14C ratios, which were not affected by dietary intake. It appears that brain cholesterol level is maintained mainly by synthesis in situ and not by uptake from dietary or other sources.

Acetates↗
PubMed1984

Morphometric study of hepatocytes containing hepatitis B surface antigen.

The development of hepatocellular carcinoma (HCC) is probably related to infection with hepatitis B virus (HBV). Hepatocytes in livers of patients with HCC have been reported to show putative preneoplastic changes such as hyperplasia, dysplasia, or adenomatous regeneration. To determine quantitatively whether these morphologic changes are associated with HBV-infected cells, the authors performed morphometry of hepatitis B surface antigen (HBsAg)-positive hepatocytes in the nontumorous portion of 10 livers with HCC and in 10 livers without HCC. The diameter of nuclei and cytoplasm of HBsAg-positive hepatocytes was measured after demonstration of HBsAg by the peroxidase-antiperoxidase method. As controls, HBsAg-negative hepatocytes in the same liver sections were measured as well as hepatocytes of 20 age-matched HBsAg-negative patients with normal liver or alcoholic cirrhosis. HBsAg-positive hepatocytes exhibited significantly larger nuclei and a higher nucleocytoplasmic ratio than control hepatocytes. In addition, HBsAg-positive cells were often arranged in foci that consisted of two cell populations: hypertrophic (enlarged nuclei and nucleocytoplasmic ratio) and hyperplastic (two-cell-thick plates of small cells with a high nucleocytoplasmic ratio). While precancerous cells have been difficult to identify, these morphologic changes are frequently associated with the development of malignant neoplasia.

Carcinoma, Hepatocellular↗
PubMed1984

Pharmacokinetics in blood IV: unusual distribution, storage effect and metabolism of methotrexate.

The whole blood from three human subjects, one dog and four rabbits was spiked with methotrexate (MTX) to yield appropriate concentrations, and was incubated at 37 degrees C and 50 oscillations per min. MTX was found to exhibit unusual distribution kinetics in whole blood; plasma MTX concentrations generally dropped to a minimum at about 5 min then increased and fluctuated somewhat irregularly afterwards. Differences of up to 21, 19 and 32% between maximum and minimum were found in the studies from human, dog and rabbit, respectively. These unusual distribution phenomena might be due to the Schiff base formation between free primary amino group(s) of MTX and free fatty aldehyde groups on blood cell membrane. Similar unusual distribution kinetics were observed with blood from three human subjects after kept at room temperature or in the refrigerator, and blood collected from three dogs after intravenous bolus or infusion of MTX. Formation of three metabolites including 7-hydroxymethotrexate was only found in blood from rabbits, but not from humans and dogs.

Animals↗
PubMed1984

A specific HPLC assay to determine the pharmacokinetics of methotrexate in patients.

The pharmacokinetics of methotrexate and its metabolite, 7-hydroxymethotrexate (7-OH-MTX), were evaluated by a specific HPLC assay in patients receiving low dose (40 mg/m2) or high dose (750-1500 mg/m2) MTX. A wide range of total body clearance (1.03-5.13 ml/min/kg) was obtained in four subjects. The apparent renal clearances of MTX and 7-OH-MTX were found to decline with increasing serum levels, indicating the existence of saturable tubular secretion for the drug. The steady-state volume of distribution of MTX was 0.41-0.95 l/kg. Urinary excretion of MTX was almost complete at 36-48 h after dosing. The nonrenal excretion accounted for 17-39% of the dose. Extensive formation of 7-OH-MTX occurred at all dose levels, with their serum levels being 2.4- to 10-fold higher than MTX levels 24 h post infusion. The mean apparent renal clearance of 7-OH-MTX (0.08-0.13 ml/min/kg) was much smaller compared with that of MTX (0.63-2.62 ml/min/kg). The average saliva/serum level ratios were 0.009 and 0.078 in two patients studied.

Adolescent↗
PubMed1983

Analysis of erythromycin in biological fluids by high-performance liquid chromatography with electrochemical detection.

A simple and sensitive high-performance liquid chromatographic assay was developed for the quantitative determination of major erythromycin components and their potential metabolites or degradation products in plasma and urine. An ether extract of alkalized plasma sample was chromatographed on a reversed-phase column and the components in the column effluent were monitored by an electrochemical detector. The recovery of the drug from extraction was virtually 100%. The detection limits for erythromycin A in plasma were 5-10 ng/ml and 30 ng/ml using 1 and 0.2 ml of sample, respectively. For urine samples, a simple one-step deproteinization with two volumes of acetonitrile was satisfactory for analysis. The method has been evaluated in plasma and urine from dogs receiving oral or intravenous erythromycin A. The standard curves for potential metabolites or degradation products were not constructed due to the lack of sufficient samples.

Animals↗