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Biomedical subjects

M Xu

Publications and source records attributed to M Xu.

At least 343 records · Page 19Linked to original sources
PubMed1993

An adult-type metachromatic leukodystrophy caused by substitution of serine for glycine-122 in arylsulfatase A.

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the enzyme arylsulfatase A (ASA). We have identified a new mutation in the ASA gene of a patient with adult-type MLD. In this mutation, the glycine at position 122, a highly conserved residue in the AS gene family, was replaced by serine. In a transient expression study, COS cells transfected with the mutant cDNA carrying 122Gly-->Ser did not show an increase of ASA activity and produced little material immunoreactive to an anti-ASA antibody, despite normal mRNA levels.

Adult↗
PubMed1993

Application of tryptic condensation strategy for the synthesis of alpha-melanocyte stimulating hormone.

The use of trypsin in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) paired with N,N-dimethylformamide (DMF) has been proposed for the enzymatic condensation of peptides. The tryptic condensation strategy was applied to the synthesis of the 13-peptide, alpha-melanocyte stimulating hormone (alpha-MSH), which contains two susceptible points to trypsin, in a low-water-containing solvent system, 4% H2O in HFIP/DMF (1/1, v/v). The N-terminal 8-peptide segment (S1) ending with Arg and C-terminal 5-peptide with the side-chain protections at Lys and Trp (S2) were prepared by the stepwise coupling on p-nitrobenzophenone oxime resin and by a conventional method, respectively. Both segments were condensed by the aid of trypsin. The acid component was converted into the partially protected alpha-MSH at as high as 95% conversion determined by reversed-phase HPLC. When the side-chain of Lys at the 11-position was not protected, alpha-MSH was obtained only in 35% yield, and was contaminated with products of secondary hydrolysis. Although the Lys11-Pro12 sequence was very poorly susceptible to trypsin, the side-chain of Lys had to be protected in order to be inert to trypsin under the synthetic conditions. HFIP is demonstrated as a good solvent with DMF to allow the efficient tryptic condensation of peptides. The strategy increased the value of the enzymatic condensation as practical method by avoidance of secondary hydrolysis, high dissolution of peptides and retention of activity of enzyme.

1-Propanol↗
PubMed1993

[Preparation and identification of monoclonal antibodies against different epitopes on TAG-72 antigen].

The antigen reacted with mAb B72.3 is tumor associated glycoprotein 72 (TAG-72). It has been shown that TAG-72 has good specificity, and it can bind to TAG-72 expressed in great majority of tumors. We have prepared 2 monoclonal antibodies, named 72-45 and 72-142, against epitopes on TAG-72 antigen different from those reacted with B72.3. The results shown that both antibodies did not react with normal adult and fetus tissues but sweat and sebaceous gland and epithelial cells of small intestine. The mAb 72-45 gave a 100% (20/20) positive reaction in colon cancer and 80% (24/30) positive in lung adenocarcinoma. The mAb 72-142 showed a 40.5% (9/20) positive reaction in colon cancer and 79.5% (27/34) positive in lung adenocarcinoma. The antigenic epitopes to which mAb 72-45 directs is carbohydrate and those to mAb 72-142 is also carbohydrate, but also related to sialo-acid mucin in molecular structure.

Adenocarcinoma↗
PubMed1993

[Respiratory effects of tutin microinjection into NPBM of rabbits].

On sodium pentobarbital anesthetized, cervical vagotomized adult rabbits, the microinjection of 1 microliter (10 micrograms) tutin into NPBM causes reversible changes in electrical activity of the diaphragm in different degrees. The most remarkable change is the reversible apnea. Our results indicate that NPBM plays an important role in the generation or modulation of respiratory rhythm and that tutin stimulates the pontine respiratory related neurons, thus disturbs the activity of neuronal circuit involved in respiration rhythm generation or modulation.

Animals↗
PubMed1993

[A computer real time system for acquiring and monitoring phrenic nerve discharge signal].

This paper presents a real time system of computer (IBM PC/AT) to acquire and monitor phrenic nerve discharge signal according to the need of researching. The system was programmed with 80286 assembly language. It has the properties of fast speed, high efficiency, small size of object code and abundant interactive functions. It is easy to handle and can be used for acquiring and monitoring other electrophysiological signals.

Electrophysiology↗
PubMed1993

[An investigation of the effect of rostral ventrolateral medulla lesion on pressor response induced by electrical stimulation of hypothalamic paraventricular nucleus in the cat].

The experiments were performed on 20 adult cats anesthetized with chloralose and urethane, paralyzed and artificially ventilated. The rostral ventrolateral medulla (RVL) was explored by electrical stimulation. We found that an area, 3-5 mm rostral to the obex, 3-4 mm lateral to the midline, and 0-1 mm from the ventral surface of the medulla, was the most effective region for producing a pressor response. After bilateral microinjection of kainic acid into or electrolytic lesion of the above-mentioned active RVL area, a large decrease in arterial blood pressure was elicited, and the pressor response induced by electrical stimulation of the hypothalamic paraventricular nucleus (PA) was nearly eliminated. The results suggest that the RVL mediates the PA pressor response.

Animals↗
PubMed1993

Clinical and experimental studies on shallow needling technique for treating childhood diarrhea.

Treatment of diarrhea in children by shallow needling and by drugs was studied in 3 separate groups for comparison. For Group I, the lateral line II of the forehead was taken, i.e. the upper, middle and lower points of the line staring from Toulinqi (UB 15) vertically downwards to the place 1 cm below the hairline were selected. For Group II, shallow needling was done on body acupoints, the main points selected being Qihai (Ren 6), Shuifen (Ren 9), bilateral Tianshu (St 25), and bilateral Zusanli (St 36); the adjuvant acupoints were Taibai (Sp 3) and Gongsun (Sp 4). The depth of shallow needling was merely puncturing the skin. For Group III the drugs used were Liteling, Berberine, Gentamycin, Ampicillin, and SMZ Co. The results of treatment in Group I and II differed insignificantly, while both were significantly superior to drugs in Group III. Experimental studies also showed that shallow needling enhanced the humoral and cellular immunity and promoted the intestinal peristaltic function.

Acupuncture Therapy↗
PubMed1992

Acetylcholine receptor channel structure probed in cysteine-substitution mutants.

In order to understand the structural bases of ion conduction, ion selectivity, and gating in the nicotinic acetylcholine receptor, mutagenesis and covalent modification were combined to identify the amino acid residues that line the channel. The side chains of alternate residues--Ser248, Leu250, Ser252, and Thr254--in M2, a membrane-spanning segment of the alpha subunit, are exposed in the closed channel. Thus alpha 248-254 probably forms a beta strand, and the gate is closer to the cytoplasmic end of the channel than any of these residues. On channel opening, Leu251 is also exposed. These results lead to a revised view of the closed and open channel structures.

Acetylcholine↗
PubMed1992

Intestinal brush-border-associated enzymes: co-ordinated expression in colorectal cancer.

The brush border of normal small-intestine epithelial cells is rich in enzymes that are involved in the digestive process. Such molecules can be used as markers to analyze cell lineages and differentiation properties of colorectal cancers. Monoclonal antibodies detecting dipeptidyl peptidase-IV, aminopeptidase N, endopeptidase F, sucrase-isomaltase, alkaline phosphatase, maltase-glucoamylase and lactase have been used to analyze the phenotype of colorectal cancers, adjacent mucosa and histologically normal distant mucosa. The avidin-biotin peroxidase complex method was used. Expression of dipeptidyl peptidase-IV, aminopeptidase N, sucrase-isomaltase and alkaline phosphatase was common in non-neoplastic mucosa adjacent to, and distant from, the tumor; in contrast, endopeptidase F, maltase-glucoamylase and lactase were rarely expressed in normal distant mucosa and more frequently expressed in mucosa adjacent to the tumor. Dipeptidyl peptidase-IV, aminopeptidase N, endopeptidase F, sucrase-isomaltase and alkaline phosphatase were frequently expressed in colorectal cancers, whereas maltase-glucoamylase and lactase were rarely expressed. Two general patterns of antibody reactivity were observed: diffuse cytoplasmic and apical; apical reactivity was generally associated with more differentiated tumors. A logistic predictive regression model indicated that enzyme expression in colorectal cancers followed a coordinate pattern, but was unrelated to the location of the tumor, Dukes stage or differentiation grade. In conclusion, expression of brush-border-associated enzymes occurs frequently in colorectal cancers and is regulated in a co-ordinated manner. These markers can be used for the phenotypic sub-classification of colorectal cancers.

Alkaline Phosphatase↗
PubMed1992

How is echocardiography used? An audit of 11,701 studies.

OBJECTIVE: to review the utilisation of 2-D and Doppler echocardiography between 1984 and 1990. METHODS: analysis of request forms and echocardiogram reports for patient demographics, major clinical indications and principal echocardiogram findings. RESULTS: between May 1984 and December 1990 11,701 studies were done in 8101 patients. Requests for scans increased by an average of 225 per year. Most frequently scanned were male (55%), inpatients (52%) and patients aged 60-69 yr (19%). In 1984 cardiologists made 100% of the requests and did 78% of the studies. In 1990 noncardiologists requested 48% of scans and 91% of studies were done by technicians. Echocardiograms were requested most often for assessment of valve disease (39%), left ventricular function (18%) and congenital heart disease (15%). Thirty-five percent of studies showed valve disease, 17% myocardial disorders and 10% congenital heart disease. Normal findings were shown in 25%. CONCLUSION: in this 6.5 year period there was a rapid increase in the utilisation of echocardiography and the practice changed from one requested by and done by cardiologists to a generally available service provided by technicians. The greatest application for scanning was in the assessment of acquired valvar disease and myocardial disorders. One-quarter of echocardiograms showed normal cardiac structure and function.

Adolescent↗
PubMed1992

Granulovacuolar degeneration in the hippocampal cortex of aging and demented patients--a quantitative study.

The occurrence and topographic analysis of granulovacuolar degeneration (GVD) in the hippocampal cortex of mentally normal controls (75 cases) and patients with Alzheimer's dementia (AD; 17 cases which included Alzheimer's disease and senile dementia of Alzheimer type), multi-infarct dementia (MID; 16 cases), Pick's disease (PD; 5 cases) and atypical dementia [5 cases; non-Alzheimer, non-Pick dementia with Fahr's syndrome (NANPDF)] were investigated. GVD was rarely found in control cases below the age of 60 years. In elderly normal brains, the statistically most representative ranking order of predilection for GVD (in decreasing severity) was: in the 60 s, CA1 > prosubiculum > CA2 (no GVD was found in the CA3 and CA4); in the 70 s, CA1 > prosubiculum > CA2 > CA3 > CA4; in the 80 s, CA1 > prosubiculum > CA2 > CA3 > CA4; in the 90 s, CA1 > prosubiculum > CA2 > CA3 > CA4. In the brains of demented patients, the rank order for GVD was: for AD, CA1 > CA2 > CA3 > prosubiculum > CA4; for MID, CA1 > prosubiculum > CA2 > CA3 > CA4; for PD, CA1 > CA2 > CA3 > prosubiculum > CA4; and for atypical dementia (NANPDF), CA1 > CA2 > prosubiculum > CA3 > CA4. The similarity of the predilection to ranking order was noted both in normal aged subjects and in MID as well as both in AD and in PD.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Filarial parasites contain a ras homolog of the TC4/ran/Spil family.

We have isolated and characterized a gene encoding a novel GTP-binding protein of the GTPase superfamily in the filarial parasites Brugia malayi and Onchocerca volvulus. The deduced amino acid sequence of the cloned molecule has approximately 30% overall homology to ras proteins and approximately 90% homology to the 'ras-like' nuclear proteins TC4, ran and Spil. Rabbit antisera to bacterially expressed filarial protein detect a 24-22 kDa doublet in extracts of adult B. malayi and mature microfilariae, which is absent from immature microfilariae. Increased expression of the native parasite protein occurs when worms are cultured in the presence of epidermal growth factor.

Amino Acid Sequence↗
PubMed1992

A cloned antigen for serological diagnosis of Wuchereria bancrofti microfilaremia with daytime blood samples.

By differentially screening an adult Brugia malayi cDNA library with sera from microfilaremic and amicrofilaremic donors infected with Wuchereria bancrofti, we have identified a novel parasite antigen denoted SXP-1. Recombinant SXP-1 filarial antigen is preferentially recognized by sera from microfilaremic persons with bancroftian filariasis and from skin snip-positive patients with onchocerciasis. Antibodies to SXP-1 are restricted to the IgG4 subclass and gradually decline after treatment with diethylcarbamazine. These findings indicate that it may be possible to replace microscopic examination of night blood films with a serological test designed to detect antibodies to a mix of SXP-1 and other suitable antigens for the diagnosis of microfilaremia due to bancroftian filariasis.

Amino Acid Sequence↗