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Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 1,585 records · Page 88Linked to original sources
PubMed1967

Early effects of illumination on the activity of some photosynthetic enzymes.

Leaves of dark-grown corn (Zea mays) were illuminated for periods ranging from 3 minutes to 12 hours. The changes in the activities of ribose-5-phosphate isomerase, ribulose-5-phosphate kinase, and ribulose-1,5-diphosphate carboxylase were followed.The activity of ribose-5-phosphate isomerase did not change significantly until between 12 and 24 hours of illumination. An increase in ribulose-5-phosphate kinase activity occurred after a lag of about 6 hours. The increase in carboxylase activity began after 3 minutes of illumination and increased until after 3 to 6 hours in the light, after which it began to decline. The increases in these enzymes appear to be the result of protein synthesis.

Journal Article↗
PubMedDate not supplied

Role of vasoactive factors in the pathogenesis of early changes in diabetic retinopathy.

Several interactive and mutually perpetuating abnormal biochemical pathways, such as protein kinase C (PKC) activation, augmented polyol pathway, and non-enzymatic glycation, may be activated as a result of sustained hyperglycemia in diabetes. These abnormal pathways may in turn influence several vasoactive factors, which are probably instrumental in the production of functional and morphological changes in the retina in diabetes. The vasoactive factors such as endothelins, nitric oxide, vascular endothelial growth factors, etc., are of importance in mediating functional and structural alterations in early diabetic retinopathy. Intricate and interactive regulatory mechanism(s) among these factors may control ultimate availability of these molecules to produce biologically significant effects. A better understanding of these factors and their interactions would aid the development of adjuvant therapies for the treatment of diabetic retinopathy.

Animals↗
PubMedDate not supplied

Assessment of adrenocortical function and autoantibodies in a baby born to a mother with autoimmune polyglandular syndrome Type 2.

We describe the case of a baby born to a mother with Addison's disease in the context of Autoimmune Polyendocrine Syndrome Type 2. Adrenal cortex autoantibodies and steroid 21-hydroxylase autoantibodies were detectable in the sera of both mother and baby, suggesting the transplacental passage of these autoantibodies. Adrenal autoantibodies were present in the baby's serum at delivery, at 3, 6 and till 34 months of age but no signs of clinical or subclinical adrenal insufficiency were found in the baby during the observation period. These data suggest that the presence of adrenal autoantibodies in serum alone is not a sufficient cause for the development of autoimmune adrenalitis.

Addison Disease↗
PubMedDate not supplied

Monitoring of erythrocyte aggregate morphology under flow by computerized image analysis.

The morphology of red blood cell (RBC) aggregates was studied by direct visualization of RBC aggregation at different flow conditions in a computerized image analyzer. The aggregate morphology is expressed by an Aggregate Shape Parameter (ASP), defined as the ratio of the aggregate projected area to its square perimeter. Aggregation was induced by either dextran-70 (m.w. 70,000) or dextran-500 (m.w. 500,000), and compared to that in plasma. It was found that the aggregate morphology is a characteristic of the aggregating agent--in dextran-500, the RBC form rouleau aggregates as in plasma, while in dextran-70, they form clusters. In each system, while maintaining the overall typical morphology, the ASP decreases (i.e., the aggregate becomes longer) as the aggregate size is increased. The distribution of the ASP as a function of the aggregate size remains unchanged when the aggregate size is changed by modulation of the dextran concentration or the shear stress. Stretching of a rouleau aggregate by application of shear stress is reflected by a corresponding change in the ASP. It is suggested that the ASP is a characteristic of intercellular interactions. A theoretical model is proposed for evaluation of the deviation of aggregate shape from that of rouleau structure.

Erythrocyte Aggregation↗
PubMedDate not supplied

Purification and characterization of aromatase from human placenta.

Aromatase from human placenta has been purified to homogeneity (MW 55,000). Enzymatic activity can be reconstituted with reductase from pig liver in an aqueous buffer or after incorporation of the enzyme into liposomes. In both cases the enzyme converts androstenedione to estrone and testosterone to estradiol. Aromatase shows a typical CO-spectrum when reduced with dithionite and a type I spectral shift with both substrates. The NH2 terminal amino acid sequence is hydrophobic but shows no homology to that of other cytochromes P-450. Five cysteine peptides have been isolated by HPLC following tryptic digestion of the [14C]-carboxymethylated protein. Amino acid sequences of these peptides reveal that histidine is the carboxy-terminal amino acid of the protein and that significant homology exists with corresponding peptides from other cytochromes P-450. Unique oligonucleotides (62 and 30 MER) synthesized on the basis of a 45 amino acid sequence near the center of the molecular have been used to clone the aromatase gene from a cDNA expression library from human placenta in lambda gt11.

Amino Acid Sequence↗
PubMedDate not supplied

Electron microscopic analysis of fluorescent neuronal labeling after photoconversion.

Ultrastructural visualization of non-electron-dense fluorescent retrograde neuronal labeling was attempted by means of photo-oxidation. This procedure was used to convert the fluorescence of neurons labeled by the tracers propidium iodide, rhodamine latex microspheres and fluorogold into a stable diaminobenzidine reaction product. The ultrastructural study revealed an accumulation of electron-dense material in these cells both within lysosomes and scattered in the cytoplasmic matrix. Comparison with several different sets of control samples indicated that this material, on the basis of its amount, electron density and appearance, specifically represents the photoconversion reaction product. The effects of the intensity of the fluorescent labeling and of a prolonged photoconversion on the fine structural features of the reaction product are also described and discussed. The present findings indicate that photoconversion can be effectively applied to ultrastructural study of fluorescent retrogradely labeled neurons. The specificity of the photoconversion reaction product should be tested routinely for each fluorochrome and tissue sample.

Amidines↗
PubMedDate not supplied

Neuroglial-mediated immunoinflammatory responses in Alzheimer's disease: complement activation and therapeutic approaches.

Increasing evidence points to A beta-containing senile plaques as primary etiological agents in Alzheimer's disease (AD). The mechanism by which these deposits cause neurotoxicity is unresolved, but there are compelling data suggesting that the activated glia found associated with senile plaques contribute to the pathology of AD. These cells appear to release a variety of immunoinflammatory molecules, including complement proteins whose activation products colocalize with senile plaques and dystrophic neurites. Previous studies showed that A beta can bind and activate complement protein C1q, providing a plausible explanation for the initiation of the complement cascade in AD. Data presented here further define the nature of A beta-C1q association, revealing key aspects of the C1q domain involved in binding the amyloid peptide. Moreover, we show that it is possible to inhibit A beta-induced complement activation without affecting the normal immunoglobulin-mediated complement pathway. This indicates that it should be feasible to develop drugs to reduce complement damage in AD without compromising this important immune-defense mechanism throughout the body.

Alzheimer Disease↗
PubMedDate not supplied

The evolutionary tangle of aging, sex, and reproduction and an experimental approach to its molecular dissection.

Exchange of genetic materials by two individual members of the same species is considered to be the origin of primitive sex. During evolution, this primitive form of molecular sex has been transformed into a complex biological function involving specialized sexual structures and multiple hormonal interactions. Development and maintenance of these reproductive structures are also dependent on hormones and hormone receptors. Furthermore, reproductive specialization in higher forms of life has led to customized species-specific rates of aging and life-span potentials that are commensurate with the reproductive needs of the particular type of organism. Because of this reproductive imposition on aging of the organism, temporal regulation of the hormone response is a significant component of the genetics of aging. We have observed a marked age-dependent alteration in the hepatic expression of the rat androgen receptor (rAR) gene. Among the large number of transcription factors that control the rAR gene, at least three appear to participate in its age-dependent regulation. Two of these are positively acting and yet/to be characterized transcription factors, while the third is a negative regulator the nuclear factor kappa B (NF-kappa B). NF-kappa B is the major trans-regulator for genes involved in the immune response, inflammation, and oxidative stress. Involvement of NF-kB in the modulation of both oxidative stress and sex function provides the first example of a common molecular link between sex and aging.

Aging↗
PubMedDate not supplied

Parvalbumin and calbindin in the rat claustrum: an immunocytochemical study combined with retrograde tracing frontoparietal cortex.

The distribution of the calcium binding proteins parvalbumin and calbindin D-28k was examined in the claustrum of the rat by means of immunohistochemistry. The two proteins displayed a different and largely complementary pattern of distribution. Parvalbumin-immunostaining was intense in the neuropil of the dorsal claustrum and virtually absent in the neuropil of the ventral claustrum; parvalbumin-immunoreactive neuronal cell bodies were relatively numerous in the dorsal claustrum and were detected only occasionally in the ventral region. On the other hand, calbindin-immunostaining was prevalent in the ventral claustrum; very few calbindin-positive neurons were seen in the dorsal sector of the nucleus, whereas they were relatively more numerous in the ventral claustrum. The cell bodies of the majority of the claustral parvalbumin- or calbindin-immunoreactive neurons were oval or round, but immunostained polymorphous neurons were also observed. The surface of the immunopositive dendritic branches was smooth, with no evidence of spines. Fluorescent retrograde tracing was combined with immunohistofluorescence to determine whether the parvalbumin-containing claustral cells project to the frontoparietal cortex. Neurons labelled after large fluorogold injections in frontoparietal cortical fields were highly intermingled in the dorsal claustrum with parvalbumin-immunoreactive cells but the two neuronal populations were separate. These data show that parvalbumin-immunoreactive claustral neurons do not project to the frontoparietal cortex. In addition, although these cells may project to other cortical or subcortical targets, the present findings suggest that they may represent, at least in part, local circuit claustral neurons, corresponding to the aspiny intrinsic neurons described in the rat claustrum in studies based on Golgi impregnation.

Animals↗
PubMedDate not supplied

Association between IgE antibody against soluble egg antigen and resistance to reinfection with Schistosoma japonicum.

There is evidence that immunoglobulin (Ig) E antibody may be a critical component of protective immunity against Schistosoma mansoni and S. haematobium reinfection. In the present study, 555 individuals aged 3-67 years infected with S.japonicum received praziquantel treatment before the transmission season commenced; 45 d later, blood samples from 265 individuals who had no S. japonicum egg in their stool were examined by enzyme-linked immunosorbent assay for specific isotypic antibodies. Single, non-conditional logistic regression analysis showed that exposure intensity, age, soluble egg antigen (SEA)-IgE, SEA-IgM and soluble adult worm antigen-IgG4 were relevant to reinfection; multiple, non-conditional logistic regression analysis showed that exposure intensity was still a significant factor for reinfection while the SEA-IgE antibody level was associated with resistance to reinfection with S. japonicum, with a protective index of 2.00. It is suggested that this population in an area endemic for schistosomiasis japonica exhibits acquired immunity.

Adolescent↗