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Biomedical subjects

K Chen

Publications and source records attributed to K Chen.

At least 343 records · Page 19Linked to original sources

A new urea sensor based on combining the surface acoustic wave device with urease extracted from green soya bean and its application--determination of urea in human urine.

The urea sensor was prepared by combining a surface acoustic wave (SAW) device, in which a SAW resonator operating at 61 MHz and a pair of parallel electrodes were used in series, with urease extracted from green soya bean. The Michaelis constant and maximum reaction rate of the urease were estimated as 2.14 mM and 27.18 kHz min-1, respectively, at pH 7.0 and 25.0 degrees C. Influences of pH, temperature and effectors on the response properties of the SAW urea sensor were investigated. Recovery of the sensor ranged from 95 to 105% and the detection limit of urea was 1.0 micrograms ml-1 (1.7 x 10(-5) M). The proposed sensor has been successfully applied to the rapid determination of urea in human urine samples. The results are consistent with the reported values and also support the clinical diagnosis.

Acoustics↗

Behaviour of surface acoustic wave interdigitated array electrode sensor in non-aqueous solution and determination of blood plasma recalcification time.

A novel SAW-IDA sensor system was constructed for the first time by connecting the IDA electrodes in series with a SAW resonator. The frequency characteristics of the SAW-IDA sensor in non-aqueous solution were investigated. The effects of the parallel capacitance and cell constant were studied, and were calculated with the circuit network theory. These calculations provide guiding rules for design of the SAW-IDA sensor system. The SAW-IDA sensor was applied to determination of recalcification time and activated partial thromboplastin time of blood plasma. The sensor offers a new and effective way of studying clinical and laboratory haemostasis.

Acoustic Stimulation↗

Molecular neuroanatomy of human monoamine oxidases A and B revealed by quantitative enzyme radioautography and in situ hybridization histochemistry.

Monoamine oxidases are key enzymes in the metabolism of amine neurotransmitters and neuromodulators and are targets for drug therapy in depression, Parkinson's and Alzheimer's diseases. Knowledge of their distribution in the brain is essential to understand their physiological role. To study the regional distribution and abundance of monoamine oxidases A and B in human brain, pituitary and superior cervical ganglion, we used quantitative enzyme radioautography with radioligands [3H]Ro41-1049 and [3H]lazabemide, respectively. Furthermore, 35S-labelled oligonucleotides complementary to isoenzyme messengerRNAs were used to map the cellular location of the respective transcripts in adjacent sections by in situ hybridization histochemistry. A markedly different pattern of distribution of the isoenzymes was observed. Highest levels of monoamine oxidase A were measured in the superior cervical ganglion, locus coeruleus, interpeduncular nucleus and ventromedial hypothalamic nucleus. The corresponding messengerRNA was detected only in the noradrenergic neurons of the superior cervical ganglion and locus coeruleus. In contrast to rat brain, monoamine oxidase B was much more abundant in most human brain regions investigated. Highest levels were measured in the ependyma of ventricles, stria terminalis and in individual hypothalamic neurons. Monoamine oxidase B transcripts were detected in serotoninergic raphe neurons, histaminergic hypothalamic neurons and in dentate gyrus granule cells of the hippocampal formation. We conclude that [3H]Ro41-1049 and [3H]azabemide are extremely useful radioligands for high-resolution analyses of the abundance and distribution of catalytic sites of monoamine oxidases A and B, respectively, in human brain sections. From levels of messenger RNA detected, the cellular sites of synthesis of the isoenzymes are the noradrenergic neurons of the locus coeruleus (for monoamine oxidase A) and the serotoninergic and histaminergic neurons of the raphe and posterior hypothalamus, respectively (for monoamine oxidase B). The combination of quantitative enzyme radioautography with in situ hybridization histochemistry is a useful approach to study, with high resolution, both the physiology and pathophysiology of monoamine oxidases in human brain.

Aged↗

Two new lignans, interiotherins A and B, as anti-HIV principles from Kadsura interior.

Two new lignans, interiotherins A (1) and B (2), along with two known lignans, angeloylgomisin R (3) and schisantherin D (4), were isolated from Kadsura interior. Their structures and stereochemistries were determined from spectral data. Compounds 1 and 4 inhibit HIV replication with EC50 values of 3.1 and 0.5 micrograms/mL, respectively.

Anti-HIV Agents↗

Influence of C terminus on monoamine oxidase A and B catalytic activity.

Monoamine oxidase (MAO) A and B play important roles in the metabolism of neurotransmitters and dietary amines. The domains important for enzyme specificities were studied by construction of chimeric MAOA/B enzymes. Exchange of the N-terminal 45 amino acids of MAOA with the N-terminal 36 residues of MAOB (chimeric enzymes B36A and A45B) resulted in the same substrate and inhibitor sensitivities as the wild-type MAOA or B. Thus, the N terminus may not be responsible for MAOA or B enzyme specificities. When MAOB C-terminal residues 393-520 were replaced with MAOA C-terminal residues 402-527 (chimeric B393A) catalytic activity was not detectable. Chimeric B393A consists of eight residues with different charges, three less proline residues (458, 476, and 490), and one additional proline at 518 compared with wild-type MAOB. These differences may have induced conformational changes and affected MAOB catalytic activity. Thus, the C terminus of MAOB is critical for maintaining MAOB in an active form. It is interesting that when the C terminus of MAOA was switched with MAOB (chimeric A402B), little effect was observed on MAOA catalytic activity. This new information is valuable for further studies of the structure and function relationship of this important enzyme.

Amino Acid Sequence↗

Alanyl-glutamine dipeptide-supplemented parenteral nutrition improves intestinal metabolism and prevents increased permeability in rats.

OBJECTIVE: The authors determined the effects of alanyl-glutamine-supplemented total parenteral nutrition (TPN) on mucosal metabolism, integrity, and permeability of the small intestine in rats. METHODS: Male Sprague-Dawley rats were randomized to receive TPN supplemented with a conventional amino acids mixture (STD group) or the same solution supplemented with alanyl-glutamine; both solutions were isocaloric and isonitrogenous. On the seventh day of TPN, D-xylose and fluorescein isothiocyanate (FITC)-dextran were administered orally. One hour later, superior mesenteric vein (SMV) D-xylose and plasma FITC-dextran concentration were measured. Intestinal blood flow and calculated intestinal substrates flux were measured with ultrasonic transit time flowmetery. RESULTS: Plasma FITC-dextran increased significantly in the STD group. Intestinal blood flow and SMV D-xylose concentration did not differ between the groups. Mucosa weight, villus height, mucosal wall thickness, mucosal protein, and DNA and RNA content in jejunal mucosa were significantly increased in the alanyl-glutamine group. Jejunal mucosal glutaminase activity and net intestinal uptake of glutamine (glutamine flux) were significantly higher in the alanyl-glutamine group as compared with the STD group. CONCLUSION: Addition of alanyl-glutamine dipeptide to the TPN solution improves intestinal glutamine metabolism and prevents mucosal atrophy and deterioration of permeability.

Animals↗

Potent CD14-mediated signalling of human leukocytes by Escherichia coli can be mediated by interaction of whole bacteria and host cells without extensive prior release of endotoxin.

How invading microorganisms are detected by the host has not been well defined. We have compared the abilities of Escherichia coli and lipopolysaccharides (LPS) purified from these bacteria to prime isolated neutrophils for phorbol myristate acetate-stimulated arachidonate release, to trigger respiratory burst in 1% blood, and to increase steady-state levels of tumor necrosis factor alpha mRNA in whole blood. In all three assays, bacteria were > or = 10-fold more potent than equivalent amounts of LPS and could trigger maximal cellular responses at ratios as low as one bacterium per 20 to 200 leukocytes. Both E. coli and LPS-triggered responses were enhanced by LPS-binding protein and inhibited by an anti-CD14 monoclonal antibody and the bactericidal/permeability-increasing protein (BPI). However, whereas O polysaccharide did not affect the potency of isolated LPS, intact E. coli carrying long-chain LPS (O111:B4) was less potent than rough E. coli (J5). Furthermore, material collected by filtration or centrifugation of bacteria incubated under conditions used to trigger arachidonate release or chemiluminescence was 5- or 30-fold less active, respectively, than whole bacterial suspensions. Extracellular BPI (not bound to bacteria) inhibited bacterial signalling, but BPI bound to bacteria was much more potent. Taken together, these findings indicate that E. coli cells can strongly signal their presence to human leukocytes not only by shedding LPS into surrounding fluids but also by exposing endotoxin at or near their surface during direct interaction with host cells.

Acute-Phase Proteins↗

Speaker identification using time-delay HMEs.

In this paper, we extend the Hierarchical Mixture of Experts (HME) to temporal processing and explore it for a substantial problem, that of text-dependent speaker identification. For a specific multiway classification, we propose a generalized Bernoulli density instead of the multinomial logit density to avoid the instability during training. Time-delay technique is applied for spatio-temporal processing in the HME and a combining scheme is presented for combining multiple time-delay HMEs in order to complete a multi-scale analysis for the temporal data. Using the time-delay HME along with the EM algorithm as well as the combination of multiple time-delay HMEs, the speaker identification system has a good performance and yields significantly fast training. We have also addressed some issues about the time-delay techniques in the HME.

Algorithms↗

Kinin-mediated antihypertensive effect of captopril in deoxycorticosterone acetate-salt hypertension.

On the basis of evidence suggesting the activation of the kallikrein-kinin system in steroid-induced hypertension, we considered the possibility that the angiotensin-converting enzyme inhibitor captopril would lower the arterial blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertensive rats through kininase II inhibition. In conscious DOCA-salt hypertensive rats with intact kidneys (n = 6) or uninephrectomized rats (n = 5), the short-term administration of captopril (8 mg/kg IV) decreased mean blood pressure from 141 +/- 3 to 118 +/- 3 mm Hg (P < .05) and from 176 +/- 12 to 158 +/- 15 mm Hg (P < .05), respectively. The maximal effect of captopril was manifested between 40 and 50 minutes after its administration, and blood pressure remained depressed for at least 2 hours. The bradykinin B2 receptor antagonist Hoe 140 (500 micrograms/kg IV) abolished the antihypertensive effect of captopril in the DOCA-salt hypertensive rats, indicating kinin involvement. Losartan, an angiotensin type 1 receptor antagonist, had no effect on blood pressure in another group of DOCA-salt hypertensive rats (n = 9) and did not significantly change the response to captopril. No effect of the angiotensin-converting enzyme inhibitor was seen in normotensive control rats (n = 5), indicating the absence of a nonspecific hypotensive action of the drug. Plasma renin activity was lower in the DOCA-salt hypertensive rats (0.7 +/- 0.2 ng angiotensin I/mL per hour, n = 4) than in normotensive control rats (8.8 +/- 1.7, n = 4). The involvement of kinins in the antihypertensive effect of captopril in DOCA-salt hypertension supports the contention that the kallikrein-kinin system contributes to blood pressure regulation in this hypertension model.

Angiotensin II↗

Selection of murine lymphoid and hematopoietic cells using polystyrene tissue culture devices containing covalently immobilized antibody.

We have established rapid procedures that negatively deplete and positively select for specific murine cell populations. By using polystyrene tissue culture flasks containing a covalently bound mouse anti-rat antibody and specific anti-mouse, cell-surface antigen antibodies, we easily and efficiently depleted greater than 90% of the mature lineage cells from murine bone marrow. This selection procedure resulted in an enrichment of progenitor colonies (CFU-Cs) in murine bone marrow. Using the same polystyrene tissue culture devices, we can directly isolate CD117+ (c-kit+) murine hematopoietic cells. As few as 2000 of these CD117+ cells rescued and reconstituted lethally irradiated recipients in a murine bone marrow transplant model.

Animals↗

Missionaries and the early development of nursing in China.

By the late 1930s, nursing, which had come into being in China in the 1880s, had developed into a profession represented by a well-organized national association with a membership of 6,000, which was continuously expanding by hundreds of new recruits trained at nearly 200 nursing schools all over the country. The progress was remarkable. In retrospect, we can easily discern the outstanding contribution made by the Western medical missionaries. To the latter's dedication, the profession owed its birth and its incipient growth in particular. Trained missionary nurses, following in the footsteps of missionary pioneers, penetrated into all parts of the country to start dispensaries and hospitals literally from nothing. In 1923, China had 53 percent of the missionary hospital beds and 48 percent of the missionary doctors in the world. Missionary nurses constituted 32 percent of the total number of nurses in China in 1923 and their number reached a peak of nearly 700 in 1927. Although the number of medical missionaries, physicians, and nurses was tiny compared to the size of the nation's population, and although their interest in "healing the sick" aimed to serve their primary goal of "saving the soul," their contribution to nursing development in China, especially their efforts in training native nurses at numerous missionary hospitals and nursing schools, can hardly be overestimated. Derived from missionary involvement was another important contributor to the rapid progress of nursing: the Nurses' Association of China. Born in a critical stage of nursing development in the country, the NAC organized the profession and regulated its training through sponsoring registration, holding examinations, and developing a standard required curriculum. Essentially, it played the role of a great organizer and paved the way for the further growth of the profession. Coming from a totally different culture, missionaries had to overcome a lot of difficulty to adapt themselves to the environment in China. The problems they encountered varied from place to place. Geographically, the interior areas were more prone to antiforeign and anti-Christian feelings, whereas the coastal areas were, comparatively, more receptive to new ideas and techniques brought by Western missionaries. Fluctuating with the political developments in China, the missionaries' cause peaked when the nation welcomed them following the quelling of the Boxer upheaval and the overthrow of the dynastic monarchy, and ebbed when xenophobia or nationalism ran high in any form of massive political turmoil.(ABSTRACT TRUNCATED AT 400 WORDS)

China↗

[Clinical study on the effect of shuxuening tablet in treatment of coronary heart disease].

Shuxuening was made of extract of Folium Ginkgo, the Shuxuening tablet No. 2 was a pure extract and No. 1 was a crude extract. Forty-six coronary heart disease patients were divided randomly into two groups according to the ratio of 2:1, Shuxuening tablet No. 1 and No. 2 were given to the two groups respectively. Results showed that both of them could alleviate the symptom of angina, the total effective rate of 2 groups were 60.00% and 83.87%, there was no significant difference between the two groups. But for the angina of middle and severe degree, the total effective rate of No. 2 was 83.33%, while that of No. 1 was 33.33%, the difference was significant (P < 0.01). They could also improve the abnormal electrocardiogram, the total effective rate of two groups were 60.00% and 74.19%, no significant difference between them was found. The two drugs could decrease the blood lipid as well.

Aged↗

Genetic heterogeneity in hereditary breast cancer: role of BRCA1 and BRCA2.

The common hereditary forms of breast cancer have been largely attributed to the inheritance of mutations in the BRCA1 or BRCA2 genes. However, it is not yet clear what proportion of hereditary breast cancer is explained by BRCA1 and BRCA2 or by some other unidentified susceptibility gene(s). We describe the proportion of hereditary breast cancer explained by BRCA1 or BRCA2 in a sample of North American hereditary breast cancers and assess the evidence for additional susceptibility genes that may confer hereditary breast or ovarian cancer risk. Twenty-three families were identified through two high-risk breast cancer research programs. Genetic analysis was undertaken to establish linkage between the breast or ovarian cancer cases and markers on chromosomes 17q (BRCA1) and 13q (BRCA2). Mutation analysis in the BRCA1 and BRCA2 genes was also undertaken in all families. The pattern of hereditary cancer in 14 (61%) of the 23 families studied was attributed to BRCA1 by a combination of linkage and mutation analyses. No families were attributed to BRCA2. Five families (22%) provided evidence against linkage to both BRCA1 and BRCA2. No BRCA1 or BRCA2 mutations were detected in these five families. The BRCA1 or BRCA2 status of four families (17%) could not be determined. BRCA1 and BRCA2 probably explain the majority of hereditary breast cancer that exists in the North American population. However, one or more additional genes may yet be found that explain some proportion of hereditary breast cancer.

Adult↗

[Anti-herpes simplex virus action of combined therapy with cyclocytidine and ganciclovir].

OBJECTIVE: The study was designed to investigate the combined effect of cyclocytidine (CC) and ganciclovir (GCV) on herpes simplex virus-1 (HSV-1) in cell culture. METHODS: The 50% inhibition concentrations of HSV-1 plaque formation (IC50) of CC, GCV alone and in combination were determined by the inhibitory test of plaque formation. The combined anti-HSV-1 effect of CC and GCV was evaluated by a graphic method and fractional inhibitory concentration (FIC) indexes. RESULTS: IC50 of CC and GCV was 0.19 and 0.1 micrograms/ml, respectively. The combination of CC with GCV produced significantly synergistic activity against HSV-1 in cell culture. FIC indexes were all below 0.75. The combined therapy of CC and GCV can also decrease and delay the emergence of drug-resistant variants. CONCLUSION: These results suggest that this combined therapy of CC and GCV may be a potentially effective means in the management of patients with HSV-1 ocular infection.

Ancitabine↗