Search PubMed⌕ Search

Biomedical subjects

M L Chen

Publications and source records attributed to M L Chen.

At least 145 records · Page 8Linked to original sources
PubMed1991

The role of metabolites in bioequivalency assessment. I. Linear pharmacokinetics without first-pass effect.

The estimation of bioequivalency using metabolite data was investigated for immediate release formulations with drugs exhibiting linear pharmacokinetics and no first-pass effect. This was accomplished by generating parent drug and metabolite plasma level profiles assuming formation and excretion rate-limited pharmacokinetic models with absorption rate constants obtained from bivariate normal distributions and designated random errors. Simulation results indicated that bioequivalence determination using Cmax of parent drug and metabolite was independent of the metabolite models as evaluated by confidence interval approach. However, a clear difference with respect to the outcome of bioequivalence evaluation arises depending upon the utilization of Cmax values for the parent drug and metabolite. The major reason for this disparity was attributed to the minimal effect of the absorption process for the parent drug on the formation of the metabolite. This phenomenon results in an apparent lower intrasubject variability for Cmax of the metabolite and, in turn, a tighter confidence interval for Cmax of the metabolite in comparison with the parent drug. The simulated results have been found to be in agreement with the bioequivalency data for acetohexamide, allopurinol, procainamide, and sulindac. In all cases, the interval of the 90% confidence limit for Cmax of the metabolite is always smaller than that of the parent drug, regardless of the drug pharmacokinetics and the level of error contained in the data.

Acetohexamide↗
PubMed1991

Effects of brevetoxin-B on motor nerve terminals of mouse skeletal muscle.

1. The effects of brevetoxin-B, a red tide toxin, on motor nerve terminal activity were assessed on mouse triangularis sterni nerve-muscle preparations. The perineural waveforms were recorded with extracellular electrodes placed in the perineural sheaths of motor nerves. 2. At 0.11 microM, brevetoxin-B increased the components of waveforms associated with sodium and potassium currents while it decreased the calcium activated potassium current and the slow calcium current of the nerve terminal. The fast calcium current and slow potassium current were not affected. 3. At 1.11 microM, brevetoxin-B decreased all of the components of waveforms associated with sodium, potassium and calcium currents. 4. It is concluded that brevetoxin-B affects sodium, potassium as well as calcium currents in the nerve terminal. The effects may contribute to its pharmacological actions on synaptic transmission.

Animals↗
PubMed1991

Effect of brevetoxin-B on the neuromuscular transmission of the mouse diaphragm.

The effects of brevetoxin-B, a polyether toxin isolated from Gymnodinium breve Davis, on neuromuscular transmission were studied on the mouse hemidiaphragm using general pharmacological and electrophysiological methods. Brevetoxin-B initially induced spontaneous muscle twitching followed by complete paralysis of the indirectly elicited twitch tension of the mouse diaphragm. The directly elicited muscle twitch tension was not affected and the compound action potential of the phrenic nerve could still be recorded when neuromuscular transmission was completely blocked by the toxin. Brevetoxin-B initially increased, but then decreased, the antidromic activity of the phrenic nerve. Brevetoxin-B increased the frequency of miniature endplate potentials (MEPP), while it decreased the muscle membrane potential. Application of tetrodotoxin (TTX) completely abolished the increase in MEPP frequency and the depolarization of the muscle membrane potential. The results suggested that brevetoxin-B may affect the sodium channels in the nerve terminal and muscle membrane.

Action Potentials↗
PubMed1991

Antenatal ultrasonic findings of craniofacial malformations.

Fetal craniofacial malformations were identified sonographically in 13 cases. Holoprosencephaly and median cleft syndrome were the most frequent findings. Cleft lip, cleft palate, single nostril, cyclopia and hypotelorism were also seen. Seven of the 13 cases (54%) had polyhydramnios. Amniocentesis was performed on 12 fetuses, and 5 of them showed autosomal trisomy. Accordingly, when craniofacial malformation is recognized antenatally, a careful survey of the fetus for other associated structural anomalies and cytogenetic study are indicated to aid in diagnosis and subsequent obstetric and neonatal management. Also screening for fetal craniofacial malformation is recommended during mid-trimester ultrasound examinations.

Abnormalities, Multiple↗
PubMed1991

Comparative studies on the detection of hepatitis B virus DNA in frozen and paraffin sections by the polymerase chain reaction.

The polymerase chain reaction (PCR) is an extremely sensitive technique that has been used for detection of DNA sequences in formalin-fixed, paraffin-embedded tissues. In order to verify that hepatitis B virus (HBV) DNA sequences are adequately preserved in routinely processed liver tissues, we performed PCR with five different primer pairs for HBV sequences on DNA extracted by two different methods from paraffin and frozen liver sections. The amount of PCR products obtained with DNA templates extracted by the proteinase K-SDS method from frozen sections was significantly larger than that from paraffin sections. However, boiling of deparaffinized sections in water containing Chelex-100 resulted in ample amounts of PCR products irrespective of the primers used. On Southern blots, the location of the bands of amplified DNA obtained by the different methods was consistent with the predicted size, suggesting that the viral sequences had not been altered by processing. Although freezing of fresh tissue yields quantitatively more HBV DNA, formalin fixation qualitatively preserves the viral DNA sequences adequately for detection by PCR. Therefore, formalin-fixed, paraffin-embedded tissues may be used for the detection of viral DNA sequences by PCR. Application of the described procedure to routinely processed tissues significantly broadens the applicability of this powerful diagnostic and investigative method.

Base Sequence↗
PubMed1991

Liver disease in rhesus monkeys infected with simian immunodeficiency virus.

Rhesus monkeys infected with simian immunodeficiency virus (SIV) develop a syndrome very similar to patients with acquired immune deficiency (AIDS), including liver disease. This prospective study was undertaken to define the pathology, course, and pathogenesis of liver disease in 20 rhesus monkeys (Macaca mulatta) after intravenous inoculation with the standardized isolate SIV/DeltaB670. Tissue samples from liver and gallbladder between 2 and 24 weeks after inoculation were examined histologically and immunohistochemically for SIV gag protein p26, and by in situ hybridization with an SIV riboprobe. Histologically there was infiltration of portal tracts and around hepatic veins and venules by mononuclear inflammatory cells, focal bile duct damage, proliferation of bile ductules, and focal lobular inflammation as early as 2 weeks after infection. The severity and extent of these lesions were graded semiquantitatively and showed that bile duct damage and hepatic venulitis were the most significant changes. Simian immunodeficiency virus gag protein p26 and SIV RNA were detected in scattered mononuclear cells in portal tracts and sinusoids, but not in hepatocytes or bile duct epithelial cells. The data indicate that the liver is involved early during the course of SIV infection, followed by persistent changes until the terminal stage of the disease. Our findings suggest that the liver damage in SIV-infected rhesus monkeys is similar to the changes observed previously in AIDS patients.

Animals↗
PubMed1990

Sodium-dependent phosphate transport in primary cultures of renal tubule cells from young and adult rats.

The transport of phosphate by primary cultures of renal cells from young (5-6 weeks) and adult (10-12 months) rats was studied. Renal tubule cells isolated from young and adult groups exhibited typical epithelial morphology and similar growth rates. The Na-dependent phosphate uptake was saturable with a Km of 5-7 microM over a substrate range of 1-500 microM. A decrease in Na-dependent phosphate uptake in adult cells (30%) was found compared to that of young cells. The Na-independent component of phosphate uptake did not vary with age. In addition, the inhibition of phosphate uptake by a variety of compounds (ouabain, gramicidin, 2,4-dinitrophenol, KCN, and arsenate) were similar in both age groups. Kinetic analysis showed that a significant reduction in Vmax (4.4 +/- 0.4 vs. 3.1 +/- 0.2 nmol Pi/mg protein/10 min in young and adult cells, respectively), but not Km, resulted in this decreased uptake of phosphate in adult groups. There was no difference in the efflux of phosphate from both age groups. When cells were preincubated in a phosphate-free medium for 24 hours, the uptake of phosphate was increased to 46% and 24% of their corresponding controls in young and adult cells, respectively. The decreased phosphate uptake and limited adaptation to a phosphate-free medium by the adult renal cells may account for the hypophosphatemia and phosphaturia seen in adult and old animals in vivo.

Adenylyl Cyclases↗
PubMed1990

Continuous expression and replication of the hepatitis delta virus genome in Hep G2 hepatoblastoma cells transfected with cloned viral DNA.

To establish stable cell clones allowing continuous replication of hepatitis delta virus (HDV), Hep G2, a hepatoblastoma cell line containing no hepatitis B virus (HBV) DNA sequences, was transfected with a recombinant plasmid containing a tandem trimer of HDV cDNA (driven by the simian virus 40 late promoter) and a neomycin-resistance gene. After selection with the neomycin analogue G418, at least two of the resistant clones were shown to have intact delta antigen by specific immunoblotting, and the delta antigen was located in the cell nucleus by immunofluorescence. Transfected cloned viral DNAs were found to be integrated into cell chromosomes. Replication of the HDV genome was demonstrated by the presence of not only genomic and antigenomic HDV RNAs but also HDV RNAs in multimeric and circular forms. In addition, a 0.8-kilobase antigenomic RNA containing a poly(A) tail and encoding the delta-antigen open reading frame was documented. Continuous replication and transcription of the HDV genome was thus achieved in these transfected cell lines. The results confirmed that replication of HDV was unassisted by HBV. Stable passage of such cell lines strongly suggests that HDV lacks direct cytopathicity in hepatocytes. These clones should be useful in studying the details of the HDV life cycle and the relationship between HDV and its helper virus, HBV.

Antigens, Viral↗
PubMed1990

The stability of iodine in human sweat.

The relation between the sweat iodine loss and the urinary iodine excretion was studied on 13 physically active male athletes. There were no statistical differences between the sweat iodine concentrations before and after high iodine food intake, no difference between those before and after 1-h strenuous exercise, or no difference between those of the goitrous and the non-goitrous. These results indicate that the sweat iodine concentration is quite steady and the total iodine loss per day seems to be directly related to the volume of the sweat lost in each subject. The concentration variation of sweat iodine among individuals is small. The mean concentration of 13 athletes during 8 consecutive days was about 37 +/- 6.6 micrograms/l. By comparing the iodine concentration of urine and sweat, the iodine concentration of sweat seems to be more stable than that of urine. The results indicated that the urinary iodine excretion plays a regulatory role for iodine balance in the body and that iodine appeared to be an essential constituent of sweat.

Adolescent↗
PubMed1990

[An in situ hybridization and immunofluorescent double staining study on the pathogenesis of HBV in kidney disease].

The exact role of HBV in the pathogenesis of renal lesions is still unconfirmed. In order to investigate whether HBV replicates and causes direct injury in the kidney as it does in other extrahepatic organs or acts as an antigen to cause an immune reaction, we did in situ hybridization combined with IF double staining study of kidney and liver specimens from 8 patients with HBV infection and positive HBsAg in the glomeruli. In situ hybridization was performed with 3H and biotin labelled HBV-DNA probes, their specificity was determined by verified HBV-DNA positive and negative samples as controls. DNase predigestion and HBV-DNA probe replacement Rhodamine labelled rabbit antihuman IgG, goat nati-HBsAg, FITC labelled rabbit anti-goat IgG were used for IF double-staining. Their specificity was confirmed by positive, negative controls and blocking test. The double-staining revealing HBsAg deposition was in the same position with that of IgG. HBV-DNA was not detectable in all the 8 patients even though 3 of them had HBV-DNA in the liver. It is suggested that HBV replication does not occur in the kidney, but its antigen components may cause a progressive immune reaction which results in renal damage.

DNA Probes↗
PubMed1990

The effects of myasthenic immunoglobulin G on the ultrastructure of mouse motor endplate.

The effects of immunoglobulin G (IgG), taken from a patient with myasthenia gravis (MG), were studied on the ultrastructure of mouse diaphragm. IgG from a normal patient served as control. After chronic intraperitoneal injection of IgG isolated from the normal patient, the axon terminal of the mouse diaphragm was filled with numerous synaptic vesicles, mitochondria as well as occasional bundles of fine neurofilaments and neurotubules. Primary and secondary synaptic clefts appeared normal. Similar results showed in the axon terminal of the mouse chronically injected with IgG from MG patient. No significant ultrastructure changes were found in the motor endplate of mouse injected chronically with IgG from a MG patient compared with the motor endplate of mouse injected chronically with IgG from normal patient. It is postulated that IgG from MG may not exert morphological changes on the mouse diaphragm, even after chronic intraperitoneal injection.

Animals↗
PubMed1989

Effects of memantine on the twitch tension of mouse diaphragm.

The effects of memantine (50-175 microM) on the post-tetanic potentiation of the twitch tension were studied on the isolated mouse nerve diaphragm preparation. Memantine completely abolished the twitch tension elicited indirectly while it had no effect on the directly elicited twitch tension. Memantine also decreased the post-tetanic potentiation of amplitude of endplate potential and twitch tension. The duration of tetanic stimulation that induced a maximal decrease of twitch tension was 10-20 s. It is suggested that the effect of memantine on post-tetanic potentiation may be due to its voltage- and time-dependent effect on the ion channel-acetylcholine receptor complex.

Amantadine↗
PubMed1989

Actions of dendrotoxin on K+ channels and neuromuscular transmission in Drosophila melanogaster, and its effects in synergy with K+ channel-specific drugs and mutations.

The blockade of K+ channels and enhancement of neuromuscular transmission by dendrotoxin (DTX), a convulsant peptide from mamba snake venom, were examined in normal and mutant larval preparations of Drosophila. Two-microelectrode voltage-clamp experiments showed that DTX reduced the transient K+ current, IA, in muscle membrane. This effect was suppressed by raising the Mg2+ concentration or by lowering the temperature. The interaction of DTX with Mg2+ was further analyzed at a low cation concentration, at which DTX reduced both IA and the delayed rectifier IK. These results were correlated with the action of DTX on the neuromuscular junction. Its facilitatory effect on excitatory junctional potentials (EJPs) was relatively mild but the effect was drastically enhanced when combined with certain mutations and K+ channel blocking drugs, leading to repetitive or prolonged giant EJPs. Only the mutations or drugs that reduced IK or the Ca2(+)-dependent K+ current, ICF, could yield these synergistic effects with DTX. In contrast, the abnormal EJPs caused by the mutation or drug that blocked IA were not further enhanced by DTX, indicating that DTX also affects IA at the neuromuscular junction. Thus, the A-type K+ channels in muscle and nerve terminals appeared very similar in their sensitivity to the specific toxin, drugs and mutations examined here.

4-Aminopyridine↗
PubMed1989

Degradation of zinc-metallothionein in monolayer cultures of rat hepatocytes.

The degradation of zinc-metallothionein (MT) was studied in monolayer cultures of adult rat hepatocytes. Hepatocytes were incubated overnight in serum-free medium containing either [35S]cysteine or [3H]leucine and 100 microM zinc to induce MT synthesis. Total cellular 35S-MT was measured in the heat-stable extract of cell homogenate and quantified by fast protein liquid chromatography. When zinc was removed from the medium, 35S-MT turnover was almost 3-fold faster than that of [3H]Leu protein (t1/2 = 11 and 29 hr, respectively). The decrease in the cellular level of 35S-MT reflected degradation since less than 1% of total cellular 35S-MT was secreted into the medium. The rate of MT degradation was inversely proportional to cellular zinc content. In contrast, the degradation of [3H]Leu protein was not affected by changes in cellular zinc concentration. Chloroquine, a lysosomotrophic amine, and tosyl lysine chloromethyl ketone, an inhibitor of trypsin-like neutral protease activity, inhibited 35S-MT degradation by 65% and 50%, respectively, when cells were incubated in medium with 1 microM zinc. Turnover of [3H]Leu protein, but not 35S-MT, was enhanced by insulin deprivation. These data suggest that the degradation of hepatic MT (i) is primarily regulated by cellular zinc content and (ii) occurs in both lysosomal and nonlysosomal compartments.

Animals↗
PubMed1989

Expression of cytokeratins in normal and diseased livers and in primary liver carcinomas.

Hepatocytes and bile duct epithelium express several types of cytokeratins, the characteristic intermediate-filament proteins of epithelial cells. The cytokeratin antigen expression was studied in normal and diseased livers, intrahepatic cholangiocarcinomas, and hepatocellular carcinomas by immunohistochemical methods using a panel of polyclonal and monoclonal antibodies to cytokeratins. Ten percent formaldehyde solution-fixed, paraffin-embedded sections obtained from ten patients without liver disease, 18 patients without liver disease, 18 patients with different stages of primary biliary cirrhosis, 14 patients with alcoholic hepatitis, ten patients with fatty liver hepatitis secondary to diabetes mellitus or morbid obesity, five patients with hepatocellular carcinomas, and five patients with cholangiocarcinomas were examined. The results suggested that hepatocytes and bile duct epithelium retain their distinct cytokeratin profiles in liver disease, including malignant transformation. Therefore, demonstration of cytokeratins in the liver is useful in establishing the cellular origin of neoplasms and understanding the pathogenesis of liver diseases.

Adenoma, Bile Duct↗
PubMed1989

Effects of dietary polyunsaturated fatty acid on platelet aggregation in rats.

In the present study, we changed the fatty acid profile in blood and platelet membranes by dietary manipulation, and examined the effect on platelet aggregation in rats. Fifty-five rats were divided into five groups and fed for 56 days with 1% cholesterol and different types of fatty acid-rich diets: basal, lard, lard + fish oil, soybean oil, and soybean oil + fish oil. a decrease in serum arachidonic acid (20:4, omega-6, AA) and an increase in serum eicosapentaenoic acid (20:5, omega-3, EPA) were found in all experimental dietary groups fed with refined fish oil. Similar changes in the polyunsaturated fatty acids were also found in the platelet membrane phospholipids. Platelet aggregation, quantitated by the slope and height of the aggregation curve induced by different concentrations of ADP in a platelet aggregometer, was inhibited in all groups fed with refined fish oil. This inhibition of platelet aggregation may be related to an increase in the ratio of EPA and AA in the platelet membrane phospholipids after dietary manipulation. The differences in the platelet aggregation and thromboxane B2 (TXB2) concentration between the lard and the lard + fish oil groups were more profound than that between the soybean oil and the soybean oil + fish oil group. However, the malondialdehyde (MDA) concentration revealed no significant differences between the five groups.

Animals↗
PubMed1989

[Detection of HBV DNA in hepatocellular carcinoma by in situ hybridization using a biotin-labelled probe].

Eight cases of hepatocellular carcinoma were hybridized in situ with a biotin-labelled HBV DNA probe on formalin fixed paraffin embedded sections. HBV DNA was detected in 218 cases both in cancer and pericancerous tissue of the liver, and both carcinomas were well differentiated. In three cases, HBV DNA was only present in pericancerous tissue and no HBV DNA could be identified in the remaining three cases. The positive rate of HBV DNA was 25% in tumor and 62.5% in the pericancerous area of liver. HBcAg was negative in all the eight tumors, nevertheless, HBsAg was present in one case. Both HBsAg and HBcAg were positive in the peri-cancerous tissue of liver in 6 out of 8 cases. In the remaining two, one was only HBsAg positive while the other was HBcAg positive. HBV DNA was identified mainly in the cytoplasm of tumor cells. In certain cells it was seen in the perinuclear cytoplasm or beneath the nuclear envelope. Only in a few cells, HBV DNA was distributed in the nuclei diffusely. Since HBV DNA was present both in the cytoplasm and nuclei, suggesting that HBV DNA was present in either integrated or free forms.

Adult↗