Search PubMed⌕ Search

Biomedical subjects

A Krichevsky

Publications and source records attributed to A Krichevsky.

26 records · Page 2Linked to original sources
PubMed1987

Development of an assay for a biomarker of pregnancy and early fetal loss.

Human chorionic gonadotropin (hCG) is a glycoprotein hormone, secreted by the syncytiotrophoblast cells of the fertilized ovum, that enters the maternal circulation at the time of endometrial implantation. It is composed of two nonidentical subunits; alpha and beta, with molecular weights of 14 kD and 23 kD, respectively. Its alpha subunit is identical in primary structure to its glycoprotein homologs, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). Human chorionic gonadotropin binds to the same receptor as hLH and displays the same biological response, namely, to stimulate the declining function of the corpus luteum to produce progestins and estrogen late in the menstrual cycle. The differences in the structures of hCG and hLH have been exploited to develop antibodies that can measure hCG specifically in the presence of hLH. Two-site antibody binding assays have been developed, based on a surface immunological concept of hCG epitopes, that involve four distinct regions to which antibodies against hCG can bind simultaneously. Antibody cooperative effects, in conjunction with kinetic advantages derived from the concentration factors by use of the sandwich assay technique (immunoradiometric assay, IRMA), have enabled development of extremely sensitive and specific measurement protocols for urinary hCG. The assay described herein permits the detection of pregnancy on an average 25.4 days after the first day of the preceding menses, as opposed to 29.5 days for conventional radioimmunoassay techniques. In addition, the greater sensitivity and specificity of this assay method has permitted the detection of episodes of fetal loss not detected by radioimmunoassay of urine specimens. A large scale epidemiological study is in progress using this assay technique as a way to identify pregnancies that are lost before becoming clinically apparent. This methodology provides a valuable tool for the determination of the rate of early fetal loss.

Amino Acid Sequence↗
PubMed1987

Flow cytofluorometric analysis of choriogonadotropin-like material on the surface of human and mouse malignant cells.

Quantitation by flow cytofluorometry of the distribution of human choriogonadotropin (hCG)-like material on the surface of various human and mouse tumor cells grown in tissue culture and as solid tumors has been done using fluorescein-tagged rabbit antisera (IgG fraction) to intact hCG and, in one experiment, by use of two monoclonal antibodies specific for hCG. Fibroblasts were used as a negative (nontumorigenic) cell control, and a rabbit antiserum to human hemoglobin was used as reagent control. All malignant cells tested stained more intensely with the anti-hCG serum than with the antihuman hemoglobin serum. Positive reaction with the monoclonal antibodies specific for hCG provided strong evidence that the material stained was identical to hCG. Heterogeneity of the expression of the hCG-like material was notable both within each cell line and between different cell lines. This heterogeneity was not associated with cell-cycle phase. 3T3 fibroblast-like cells in vitro were originally negative for hCG but acquired reactivity with anti-hCG serum after ten passages.

Animals↗
PubMed1985

Characterization and relative orientation of epitopes for monoclonal antibodies and antisera to human chorionic gonadotropin.

We analyzed ten monoclonal antibodies and three polyclonal antisera directed against human chorionic gonadotropin by immunoassay in order to determine which pairs of antibodies are capable of binding simultaneously to hCG. A relative orientation of epitopes on the surface of hCG could be inferred from a matrix of data describing the abilities of particular antibody pairs to inhibit competitively or enhance the binding of each other. These results indicated that the binding site of each of the antibodies could be assigned to one of three different regions of the hCG molecule, and at least one antibody binding within each region exhibited a substantial preference for hCG relative to human luteinizing hormone. One of these regions is the COOH-terminal portion of the hCG beta subunit. A second region contains the binding site for the SB6 rabbit antiserum (which has been widely employed in clinical studies) as well as the binding sites of several monoclonal antibodies. Antibodies to this second region characteristically bind both the whole hormone and the free beta subunit. A third region contains the binding sites of a previously reported human antiserum and also several monoclonal antibodies. These antibodies characteristically react preferentially with the intact hormone relative to the free subunits. The information contained in the type of epitope map described here can be used as the rational basis for the design of two-site immunoradiometric assays for hCG and/or its subunits.

Animals↗
PubMed1983

The use of [125I]iodocyanopindolol as a specific probe for beta-adrenergic receptors in differentiating cultured rat skeletal muscle.

In order to examine more precisely the role of beta-adrenergic receptors in the process of differentiation we used the new radioligand iodocyanopindolol ([125I]ICYP), which we found to be a very useful probe to identify beta receptors. Binding characteristics conformed to those expected for a physiologically relevant beta receptor. L6E9 cells grown in horse serum, which allows differentiation, exhibit increased beta receptor density in intact cells as a function of age. In contrast, cells grown in fetal calf serum, which does not allow differentiation, exhibit constant beta receptor density. In broken cells, however, both differentiating and non-differentiating cells show an increase in beta receptors. These results suggest that the process of differentiation is associated with an unmasking of beta receptors which are increasing but cryptic in undifferentiated cells.

Adenylyl Cyclases↗
PubMed1981

Glucocorticoids enhance glucose uptake and affect differentiation and beta-adrenergic responsiveness in muscle cell cultures.

The role of glucocorticoids (GLC) in liver glycogen metabolism is well characterized; its role in peripheral tissues is not as well understood (Baxter, 1976). GLC administration in vivo is associated with hyperglycemia, but it is not clear whether decreased glucose uptake in a peripheral tissue like muscle accounts, in part, for the effect. We investigated the relationship of glucose uptake to beta-adrenergic responsiveness in muscle cell cultures exposed to GLC. Under these conditions GLC and other serum factors are present in at least a tenfold dilution relative to in vivo conditions. We observed that the GLC dexamethasone (DEX) induces a significantly enhanced Vmax for deoxyglucose uptake in the rat muscle cell lines L8 (200--400%) and L6E9 (50--100%). DEX inhibits cell fusion and promotes epithelioid morphology within the effective dose range (L8 greater than L6E9). Growth is slightly enhanced (10--20%) at 0.1--1.0 microM. In these cells DEX also inhibits intracellular beta-adrenergic-sensitive cyclic AMP accumulation and reduces basal, catecholamine-sensitive and fluoride-sensitive adenylate cyclase in cell homogenates. The effects of DEX on deoxyglucose uptake and beta-adrenergic responsiveness are both dose (1 nM--0.1 nM) and time (1--3 days) dependent, and reversible. The degree of inhibition of the beta-adrenergic system seems to be directly related to the degree of enhancement of deoxyglucose uptake. These observations suggest that the action of DEX on muscle cell glucose uptake is related to its effect on the beta-adrenergic system.

Adenylyl Cyclases↗
PubMed1981

Inhibition of beta-adrenergic responsiveness in muscle cell cultures by dexamethasone.

Cultures of two myogenic cell lines, L6E9 and L8, were grown in the absence or presence of dexamethasone. Dexamethasone (1 microM) completely inhibited the formation of myotubes. Partial inhibition (20-40%) was obtained at a concentration as low as 1 nM. Dexamethasone also inhibited beta-adrenergic responsiveness, as noted by decreases in isoproterenol-stimulated adenylate cyclase activity and cAMP accumulation. These effects were both dose and time dependent. In the presence of dexamethasone, the number of beta-adrenergic receptors, as assessed by [125I]iodohydroxybenzylpindolol binding, decreased coordinately with the decrease in cAMP. A high affinity, limited capacity cytosolic binding site for [3H]triamcinolone acetonide observed under control conditions (Kd = 0.7 nM; maximum binding, 2.7 pmol/mg protein) increased in number as a function of developmental state. These data indicate that glucocorticoids inhibit myogenesis and beta-adrenergic responsiveness in vitro.

Adenylyl Cyclases↗