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Biomedical subjects

F Lai

Publications and source records attributed to F Lai.

53 records · Page 3Linked to original sources
PubMed1991

Matrix effects in the derivatization of amino acids with 9-fluorenylmethyl chloroformate and phenylisothiocyanate.

Pre-column derivatization of amino acids is widely practiced today for the HPLC analysis of amino acids. Due to the requirement for pH control, excess reagent removal and multi-step manipulations, automation is a major challenge in the derivatization of amino acids. Another challenge for pre-column chemistries is the effect of matrices in the sample such as salts, buffers and surfactants. This paper reports on automated derivatization using phenylisothiocyanate (PITC) and compares matrix effects between this PITC method and that of derivatization using 9-fluorenylmethyl chloroformate (FMOC). An autosampler was programmed to mix amino acid samples with PITC or FMOC reagent, allow a programmed reaction time, extract excess reagent and finally inject onto the HPLC. To study sample matrix effects, amino acid samples were spiked with various concentrations of Tris-HCl, phenol, citrate, sulfosalicylic acid, sodium chloride and sodium dodecyl sulfate. Using the PITC method and the FMOC method, the recoveries of amino acids in varied sample matrices were compared to pure amino acid standards. The PITC method appears to be affected less by matrix effects than the FMOC method. However, the FMOC method has a higher sensitivity so that sample dilution (up to 30 times) can be used to eliminate matrix effects.

Amino Acids↗
PubMed1990

Electroporation of a suicide plasmid bearing a transposon into Brucella abortus.

The creation of bacterial mutants by transposon mutagenesis has facilitated the identification of regulatory and structural genes. In the case of B. abortus the number of reported transposon mutants created by mating or P1 infection has been relatively small. We studied the conditions necessary to introduce Tn5 bearing a kanamycin resistance gene (KnR) into B. abortus by electroporation. The highest frequency of Tn5 transposition was obtained using B. abortus 2308 harvested at a density of 5.2 x 10(8) cells/ml; 0.5 microgram of plasmid was electroporated for 10 ms at 625 V (equivalent to 12.5 kV/cm). The frequency of Tn5 transposition obtained under optimum conditions was estimated to be around 18-20 insertions per 10(10) Brucella. The phase of growth (or the number of generations) had a strong influence on the frequency of transposition. Dot blot analysis confirmed that all KnR clones appearing after 4 days of incubation at 37 degrees C carried Tn5 in their genomes. Furthermore, the randomnes of Tn5 insertion was verified by Southern analysis of chromosomal DNA extracted from knR clones and hybridized with labeled Tn5.

Blotting, Southern↗
PubMed1989

A prospective study of Alzheimer disease in Down syndrome.

Ninety-six individuals with Down syndrome over age 35 years were evaluated and followed up for evidence of nontreatable dementia. Dementia was judged to be present when a functional decline occurred in areas such as orientation, memory, verbal and motor skills, and self-care abilities. Forty-nine patients with Down syndrome fit this criterion, with an average onset of dementia at 54.2 +/- 6.1 years. The prevalence of dementia in the institutionalized Down syndrome population of our study (n = 53) was 8% (2/25 patients) between 35 and 49 years, 55% (11/20 patients) between 50 and 59 years, and 75% (6/8 patients) of those over 60 years old. Of note, 41 (84%) demented individuals with Down syndrome developed seizures. Ten (20%) had parkinsonian features. Adequately treated hypothyroidism was present in 27 (59%) of 46 demented patients with Down syndrome tested. The average duration of dementia in the 23 patients who died was 4.6 +/- 3.2 years. Computed tomographic scans in 43 patients all showed brain tissue loss, most pronounced in the temporal lobes. Brains from 12 autopsied cases showed large numbers of plaques and tangles in the same locations as in persons with Alzheimer disease.

Adult↗
PubMed1988

The distribution of P elements in D. melanogaster along the coast of China studied by DNA hybridization method.

The distribution of the P-M system in four local Drosophila melanogaster populations obtained in southern China has been examined by mating tests. There was no P strain. A HindIII fragment of the P element has been cloned, named as pPH 0.86, and used as probe in this study. The distribution of the P element itself in thirteen local D. melanogaster populations along the eastern coast of China has been studied by the method of DNA hybridization. It is found that all the populations obtained from the north of Shanghai carry P elements but few populations from the south of Shanghai carry P elements. In comparison with the mating test, the method of DNA hybridization is more direct and reliable. The origin and trends of distribution of P elements in China are discussed in this paper.

Animals↗
PubMed1985

Interaction of amoxapine with muscarinic cholinergic receptors: an in vitro assessment.

Amoxapine, an antidepressant with a rapid onset of therapeutic efficacy and great utility in psychotic depression, has been reported to produce anticholinergic side effects in man similar to those observed with imipramine and amitriptyline. To establish its cholinergic disposition, amoxapine and its metabolites 7-hydroxyamoxapine and 8-hydroxyamoxapine, have been evaluated by determining their effects on quinuclidinyl benzilate (QNB) binding to membrane fractions of rat and human brain, on the carbamoylcholine-stimulated accumulation of inositol phosphates in rat cerebral cortex and on the acetylcholine-induced contraction of the guinea pig ileum. In all three preparations, amoxapine was found to be a considerably weaker antagonist of muscarinic cholinergic receptors than either imipramine (4-27 fold) or amitriptyline (51-300 fold). These results indicate that for amoxapine, no correlation exists between the magnitude of muscarinic receptor inhibition and the extent of 'anticholinergic' side effects found in the clinic. Neither the metabolites of amoxapine nor species differences could account for this discrepancy.

Acetylcholine↗
PubMed1982

Dementia in Down's syndrome: observations from a neurology clinic.

Clinical manifestations of dementia were reviewed in 15 Down's syndrome (DS) patients referred to a neurological clinic over a 24-month period for mental deterioration. The ages ranged from 32-64 years. One hundred percent showed personality changes and loss of independent daily living skills, the presenting symptoms in two-thirds of the cases. Other manifestations included seizures (53%), gait deterioration (73%), sphincteric incontinence (40%), and pathological release reflexes (67%). All 7 patients with CT-scans showed moderate or severe central and peripheral cortical atrophy. Detailed clinical information is presented for two patients, one of whom showed a temporary remission with imipramine. A characteristic dementia syndrome appears to be present in a subpopulation of aging DA patients with radiographic findings of Alzheimer's disease.

Activities of Daily Living↗
PubMed1975

Early changes in myocardial hypoxia: relations among mechanical function, pH, and intracellular redox states.

When rat hearts were subjected to abrupt hypoxia the onset of NADH changes as measured by epicardial fluorescence and of depressed contractility occurred at similar times. Direct measurements of changes in tissue metabolism lagged behind changes in fluorescence and contractility. Calculated NAD:NADH ratios became reduced more rapidly and to a greater extent in the cytoplasm than in the mitochondria, but did not necessarily signal greater changes in total NADH. The detection of depressed contractility before a fall in intracellular pH or a rise in intracellular lactate casts doubt on the postulate that an increase in hydrogen ion is the primary cause of hypoxic myocardial failure.

Animals↗
PubMedDate not supplied

Morphological and biochemical assessment of DNA damage and apoptosis in Down syndrome and Alzheimer disease, and effect of postmortem tissue archival on TUNEL.

We have previously shown that Alzheimer disease (AD) brain exhibits terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) for DNA damage and morphological evidence for apoptosis. Down syndrome (DS) is a neurodegenerative disorder that exhibits significant neuropathological parallels with AD. In accordance with these parallels and the need to clarify the mechanism of cell death in DS and AD, we investigated two principal issues in the present study. First, we investigated the hypothesis that TUNEL labeling for DNA damage and morphological evidence for apoptosis is also present in the DS brain. All DS cases employed had a neuropathological diagnosis of AD. Analysis of these cases showed that DS brain exhibits a significant increase in the number of TUNEL-labeled nuclei relative to controls matched for age, Postmortem Delay, and Archival Length, and that a subset of TUNEL-positive nuclei exhibits apoptotic morphologies. We also report that Archival Length in 10% formalin can significantly affect TUNEL labeling in postmortem human brain, and therefore, that Archival Length must be controlled for as a variable in this type of study. Second, we investigated whether biochemical evidence for the mechanism of cell death in DS and AD could be detected. To address this question we employed pulsed-field gel electrophoresis (PFGE) as a sensitive method to evaluate DNA integrity. Although apoptotic oligonucleosomal laddering has not previously been observed in AD, PFGE of DNA from control, DS and AD brain in the present study revealed evidence of high molecular weight DNA fragmentation indicative of apoptosis. This represents biochemical support for an apoptotic mechanism of cell death in DS and AD.

Adult↗
PubMedDate not supplied

Heparin-induced thrombocytopenia with arterial thrombosis: an unusual case.

A case of heparin-induced thrombocytopenia with thrombosis (HITT) is described. The patient, treated for several days with porcine Ca-heparin at a dosage of 10,000 IU/day, presented severe thrombocytopenia (Plt 36 x 10(9)/L), intermittent right leg ischemia, and a positive heparin-induced platelet aggregation assay. We promptly discontinued heparin and started picotamide, an antiplatelet drug. Rapid clinical improvement was observed in a few days. We stress the unusual features of the reported case (HITT during prophylactic therapy with low doses of porcine heparin; intermittent thrombosis), and we suggest picotamide represents a rational therapy for HITT on the basis of clinical and pathogenetic considerations.

Drug Therapy, Combination↗