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Biomedical subjects

M Hu

Publications and source records attributed to M Hu.

At least 199 records · Page 11Linked to original sources
PubMed1992

3D structure determination from electron-microscope images: electron crystallography of staurolite.

Resolution of better than 2 A has been obtained in many crystals by high-resolution electron microscopy. Although this resolution is sufficient to resolve interatomic spacings, structures are traditionally interpreted by comparing experimental images with contrast calculations. A drawback of this method is that images are 2D projections in which information is invariably obscured by overlap of atoms. 3D electron crystallography, developed by biophysicists to study proteins, has been used to investigate the crystal structure of staurolite. Amplitudes and phases of structure factors are obtained experimentally from high-resolution images (JEOL ARM 1000 at the National Center for Electron Microscopy at LBL), taken in different directions from thin regions where dynamic scattering is minimal. From images in five orientations (containing 59 independent reflections to a resolution of 1.38 A), a 3D electron potential map is constructed which resolves clearly all cations (Al, Si, Fe, including those with partial occupancy) and all O atoms. This method has great potential in crystal structure determinations of small domains in heterogeneous crystals which are inaccessible to X-ray analysis. It is estimated that 3D structure determinations should be possible on regions only about ten unit cells wide and should resolve not only atom positions but also site occupancies. The method is also applicable to space-group determination.

Chemical Phenomena↗
PubMed1992

Transport of a large neutral amino acid in a human intestinal epithelial cell line (Caco-2): uptake and efflux of phenylalanine.

The processes of L-phenylalanine (Phe) uptake and efflux from the apical (AP) and basolateral (BL) sides of an intestinal epithelial cell line (Caco-2) were investigated to further characterize the mechanism of transcellular transport of this amino acid. The results indicated that the initial uptake rates of Phe were saturable with a Km of 2.7 mM for AP uptake and 0.18 mM for BL uptake. Unlike the uptake, the initial efflux rates were shown to be proportional to the intracellular concentrations of Phe. Based on these kinetic studies and determination of other characteristics (e.g., Na+ dependency) of the uptake and efflux processes, it was concluded that AP uptake, BL uptake and BL efflux were distinctly different. This suggests that either different carriers or a different combination of carriers are responsible for the transmembrane transport of this amino acid. When the results of kinetic studies of Phe uptake and efflux were used to determine the rate-limiting step in the AP-to-BL transcellular transport of this amino acid, it was concluded that the BL efflux is the rate-limiting step in the transcellular transport of Phe in the Caco-2 cell monolayers.

2,4-Dinitrophenol↗
PubMed1992

Utilization of peptide carrier system to improve intestinal absorption: targeting prolidase as a prodrug-converting enzyme.

The feasibility of targeting prolidase as a peptide prodrug-converting enzyme has been examined. The enzymatic hydrolysis by prolidase of substrates for the peptide transporter L-alpha-methyldopa-pro and several dipeptide analogues without an N-terminal alpha-amino group (phenylpropionylproline, phenylacetylproline, N-benzoylproline, and N-acetylproline) was investigated. The Michaelis-Menten parameters Km and Vmax for L-alpha-methyldopa-pro are 0.09 +/- 0.02 mM and 3.98 +/- 0.25 mumol/min/mg protein, respectively. However, no hydrolysis of the dipeptide analogues without an N-terminal alpha-amino group is observed, suggesting that an N-terminal alpha-amino group is required for prolidase activity. These results demonstrate that prolidase may serve as a prodrug-converting enzyme for the dipeptide-type prodrugs, utilizing the peptide carrier for transport of prodrugs into the mucosal cells and prolidase, a cytosolic enzyme, to release the drug. However, a free alpha-amino group appears to be necessary for prolidase hydrolysis.

Animals↗
PubMed1992

[Further observation on the ultrastructure of the sporocyst of Schistosoma japonicum].

A further observation was conducted on the ultrastructure of mother sporocyst (Ms) daughter sporocyst in the brood chamber (b-Ds), migrating daughter sporocyst (mi-Ds) and daughter sporocyst in the liver tissue (1-Ds) of Oncomelania hupensis by scanning and transmission electron microscopy. There are 5 points worthy of mention here, namely: 1. A special structure, microvilli polymerizing cisterna, is found on the tegument of 52-day-old Ms branche in all directions and a tubule-like structure is connected to the matrix of the tegument. The significance of this structure may be dealt with the metabolism and transport of the parasite. 2. The tegumental spines appear on 52-day-old Ms. 3. The function of multilaminated vesicle in the tegument of 1-Ds may be associated with the turning over of the surface coat of the larvae and the compatibility between parasite and molluscan host. 4. Abundant alpha-glycogen granules and mitochondria appear in the cytoplasm of parenchyma cell of brood chamber of Ms and Ds. It is proposed that the parenchymal cells not only served as the filling material, but also serve as the nursing cells for the regulation of asexual reproduction of the sporocysts. 5. The orientation of muscle fibers of the head of the mi-Ds and narrow node region of 1-Ds shows a well development of the inner longitudinal fibers adjacent to the outer circular muscle layer. They run anteroposteriorly or vertically from the dorsal to the ventral. The pattern of muscle fibers may account for the activity of these regions of the parasite. (Figs 1-8).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1992

[A morphological study of retinal damages by intraocular lead].

The morphological changes in the retina were observed by light and electron microscopy at intervals after implantation of lead into the vitreous of rabbit eyes. The results revealed progressive structural disorders under both modalities of examination, indicating that lead had toxic effects on the retina.

Animals↗
PubMed1991

[Sex hormone changes during the prepubertal and pubertal development of healthy boy].

The size of testis, testosterone, LH, FSH were measured in 463 healthy boys, ages 5-18 years old. Our results showed that the values of the developmental indices increased with the age, and abruptly elevated at 13 years old indicating the beginning of puberty. At 17, all has indices had achieved the level of adulthood and did not further increase. It suggested the maturity of sex development at 17. The linear correlation analysis revealed a positive correlation between LH, FSH and testosterone (P less than 0.001, P less than 0.05-0.01, separately). The kinetic curves of LH and testosterone were also similar. The rise of LH preceded one age group than that of testosterone. The correlation between LH, FSH and testis size were positive correlation (before 14, P less than 0.001, P less than 0.01, separately; after 14, no significant difference in P values) and LH was positive correlation since 5 years old, but FSH was positive correlation since 7 years old. These finding suggest that the prepubertal testicular enlargement is primarily due to the action of LH and afterwards, FSH and testosterone combined with LH also contribute to the enlargement of testes. The clinical significance of sex hormone measurement was discussed.

Adolescent↗
PubMed1991

[Measurement of blood flow in labial and palatal mucoperiosteal flap after sectioning the greater palatine arteries and with a labial mucosal arcuate incision].

This article describes a study of determining blood flow of labial and palatal mucoperiosteal flap with radionuclide Xe-133 clearance technique before and after anterior maxillary osteotomies. The main purpose of the study was to investigate the dynamic change of blood flow. The greater palatine arteries were ligated. The studies show that compensative increasing of the blood flow of labial pedicle is seen after the operation, and that decreasing of the blood flow of palatal mucoperiosteal flap is temporary. It is suggested that the section of the greater palatine arteries is feasible. Xe-133 clearance technique is easy to operate and sensitive.

Animals↗
PubMed1990

Mechanism of L-alpha-methyldopa transport through a monolayer of polarized human intestinal epithelial cells (Caco-2).

The Caco-2 model system (Hidalgo et al., Gastroenterology, 96:736-749, 1989), which is a monolayer of polarized intestinal epithelial cells grown onto a porous polycarbonate membrane, was used to study the mechanism of transcellular transport of an antihypertensive agent, L-alpha-methyldopa (L-alpha-MD). The results showed that the transport of L-alpha-MD was pH, glucose, concentration, and temperature dependent, and it could be inhibited by metabolic inhibitors (e.g., 2,4-dinitrophenol) and by amino acids (e.g., L-phenylalanine) which have an affinity for the large neutral amino acid (LNAA) carrier. In addition, the apparent kinetic constants describing the transcellular transport of L-alpha-MD were altered depending on the time interval between feeding the cells and the transport experiments (postfeeding time, PFT). The apparent maximum carrier flux (Jmax) of L-alpha-MD was significantly increased (from 155 to 547 pmol/mg protein/min) when PFT was prolonged from 8.5 to 56 hr. These results indicated that the transcellular transport of L-alpha-MD through the polarized Caco-2 cell monolayer was carrier mediated via the LNAA carrier. The similarities in the characteristics of L-alpha-MD transport exhibited by the Caco-2 model system and other intestinal models in vitro further substantiate the usefulness of this cell culture model for studying the intestinal transport of nutrients and drugs.

2,4-Dinitrophenol↗
PubMed1989

Use of the peptide carrier system to improve the intestinal absorption of L-alpha-methyldopa: carrier kinetics, intestinal permeabilities, and in vitro hydrolysis of dipeptidyl derivatives of L-alpha-methyldopa.

Intestinal permeabilities of five dipeptidyl derivatives of L-alpha-methyldopa (I) were studied by an in situ intestinal perfusion method. The dipeptides displayed a significant increase in their permeabilities compared to L-alpha-methyldopa. The increases ranged from 4 to 20 times. These results suggest that the peptide transport system is less structurally specific than the amino acid transport systems and can be used as an absorption pathway for peptide analogues. The kinetic advantage demonstrated by the dipeptide, L-alpha-methyldopa-L-phenylalanine, over the amino acid analogue, L-alpha-methyldopa, suggests that the peptide carrier would be a possible route for improving the intestinal absorption of pharmacologically active amino acid analogues. Furthermore, the preliminary results of in vitro hydrolysis studies of selected dipeptidyl derivatives indicate that the peptide carrier system could be used as a base for a prodrug strategy.

Animals↗
PubMed1989

A study of the history of the Chinese family structures.

"It is...the purpose of this paper to discuss the [Chinese] family structure by starting from the major characteristics of family structures in traditional times and moving on from there to a brief description of family structures in modern China and the directions of change in family structures in present-day China." Consideration is given to family size and interpersonal relationships.

Asia↗
PubMed1989

[Risk factors for the formation of urinary calcium-containing stones in diabetics].

Levels of 24-hour urinary calcium, magnesium, oxalate, citrate, uric acid, phosphorus and creatinine as well as urinary volume were determined in 85 patients and 81 normal subjects. Among the patients, 43 were diabetics without stone, 5 diabetics with stone and 37 with idiopathic calcium stone formation in the urinary tract. It is shown that the main risk factors involved in urinary calcium-containing stone formation are the levels of calcium, oxalate, uric acid and citrate and the volume of 24-hour urine. With the data obtained, the authors calculated the ion-activity products index of calcium oxalate and the relative probability of stone formation in the three groups of patients and the control group of normal subjects. The index in normal subjects, diabetics without stone, diabetics with stone and patients with idiopathic urinary calcium stone was 3.07 +/- 0.16, 2.90 +/- 0.25, 3.90 +/- 0.58 and 5.11 +/- 0.38 respectively. The upper limit of the relative probability in normal subjects was 0.54. Most of the patients with idiopathic urinary calcium stone (32/37) and all the 5 diabetics with stone had higher probability value than this, while most of the normal subjects (73/81) and of the diabetics without stone (39/43) had value lower than this. The results indicate that though the diabetics have higher level of urinary calcium and higher value of the product of calcium x oxalate x uric acid, they have also inhibitive factors for stone formation, such as increased level of urinary citrate. As a result, urinary stone formation will not be a frequent occurrence.

Adult↗
PubMed1989

[HPTLC scanning determination of 6 flavonoids in 166 Rhododendron species].

This paper reports a quantitative determination in the contents of flavonoids in Rhododendron leaves by HPTLC scanning method. The methanol extract of each sample was spotted on a HPTLC silica gel plate (E. Merck F254) alongside with standard substances. Using the upper layer of petroleum ether (60-90 degrees C)-ether-formic acid (62:31:7) as developing solvent I, farrerol, kaempferol and quercetin were well separated. The spots were determined by a single wavelength (366 nm) TLC-scanner, Camag model 76510. The same plate was then further developed by developing solvent II:7 ml of the lower layer of chloroform-methanol-water (7:3:1) plus 0.5 ml of formic acid to separate polystachoside, quercitrin and hyperoside. The densitometric determination of each spot was also carried out with the same scanner. The contents of 6 flavonoids in the leaves of 166 Rhododendron species were thus determined.

Chromatography, Thin Layer↗
PubMed1989

Potential problem with fluorescence polarization immunoassay cross-reactivity to vancomycin degradation product CDP-1: its detection in sera of renally impaired patients.

During the development of a homogeneous immunoassay for the antibiotic vancomycin, we observed in certain patient samples a quantitation difference between the enzyme multiplied immunoassay technique (EMIT) method and the comparison method, fluorescence polarization immunoassay (FPIA). This prompted us to evaluate the integrity of vancomycin in samples from renally impaired patients. Since it has been reported in the scientific literature that vancomycin degrades into an antibiotically inactive crystalline degradation product (CDP-1) in vitro, we developed high-performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) methods to determine whether CDP-1 is present in patient sera. HPLC and LC/MS analysis on samples from renally impaired patients positively identified CDP-1 in fresh samples. Next, we tested the cross-reactivity of three currently available vancomycin immunoassays, radioimmunoassay (RIA) FPIA, and EMIT, to CDP-1 prepared in our laboratory. Our data suggest that CDP-1 is recognized by FPIA and RIA, both polyclonal antibody-based methods, but not by EMIT, which uses a monoclonal antibody.

Chromatography, High Pressure Liquid↗