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Biomedical subjects

M Singh

Publications and source records attributed to M Singh.

At least 829 records · Page 46Linked to original sources
PubMed1989

Targeting of methotrexate-containing liposomes with a monoclonal antibody against human renal cancer.

The potential of monoclonal antibody-linked small unilamellar vesicles containing methotrexate [(MTX)SUVs] in cancer chemotherapy was investigated. (MTX)SUVs prepared by probe sonication [50 +/- 20 (SD) nm in diameter] were linked covalently to Dal K29 (an IgG1 monoclonal antibody against human renal cancer), normal mouse IgG, or a nonspecific mouse myeloma IgG1. After incubation with a human kidney cancer cell line, CaKi-1, for 2 h, Dal K29-linked (MTX)SUVs showed 6 and 8 times more binding to CaKi-1 cells than nonspecific mouse myeloma IgG1-linked (MTX)SUV or (MTX)SUVs unlinked. After incubation with Dal K29-linked ([3H]MTX)SUVs, a higher amount of radioactivity was associated with CaKi-1 cells at 37 degrees C than at 4 degrees C. Membrane immunofluorescence revealed aggregation and capping of Dal K29-linked SUVs around CaKi-1 cells after incubation at 37 degrees C for 2 h and endocytosis at 4 and 6 h. Electron microscopic examination confirmed the aggregation of Dal K29-linked SUVs on the surface of CaKi-1 cells and their presence in endocytic vesicles at 4 and 6 h. After incubation with Dal K29-linked gold containing SUVs at 37 degrees C, gold-containing SUVs were seen on the surface as well as inside endocytic vesicle of CaKi-1 cells at 2 and 4 h. A colony inhibition assay showed that Dal K29-linked (MTX)SUVs were 5 and 40 times more potent than Dal K29-MTX and equimolar amounts of free untrapped MTX in inhibiting the growth of the target CaKi-1 cells but were not toxic to a human melanoma line (that did not react with Dal K29).

Antibodies, Monoclonal↗
PubMed1989

Identification and characterization of the nifH and nifJ promoter regions located on the nif-plasmid pEA3 of Enterobacter agglomerans 333.

Small restriction fragments of the plasmid-borne Enterobacter agglomerans 333 nif region were cloned into a promoter probe plasmid as transcriptional fusions with the lacZ gene. Identification of NifA-dependent promoters was accomplished by using a compatible plasmid which constitutively expresses the Klebsiella pneumoniae nifA gene. beta-Galactosidase assays showed strong activation of the cloned E. agglomerans promoters in Escherichia coli by the heterologous K. pneumoniae nifA gene product. The positions of the promoter fragments on the corresponding restriction map were determined by Southern hybridization. As confirmed by sequencing data, the nifH and nifJ promoters are situated at opposite end-points of the nif gene group and their -24 to -12 nucleotide sequences are similar to the consensus sequence of NtrA-dependent promoters. Also, typical NifA-binding motifs are present in both promoters. The agreement of the promoter proximal regions of nifH and nifJ with the corresponding K pneumoniae sequences is about 80%. Also the upstream regions of these genes are in agreement to some extent.

Base Sequence↗
PubMed1989

A computer simulation of T2 decay effects in echo planar imaging.

The effect of spatially variant T2 decay in echo planar images has been investigated. A simple, direct method to remove T2 effects, requiring no knowledge of actual T2 values, is also reported. The method is based on taking the geometric mean of two Hermitian symmetric data points before Fourier transformation.

Computer Simulation↗
PubMed1989

Teratogenic effects of phenytoin on chick embryos.

The antiepileptic drug phenytoin was injected into the yolk sac of White Leghorn chick embryos. A dose-response study was followed by a detailed teratological study using a single dose of 3 mg. The surviving embryos were sacrificed on the 19th day of incubation. The embryos showed a generalized decrease in body weight together with a wide range of malformations. The malformations could be roughly divided into limb, craniofacial, abdominal, and ocular defects, as well as deficiencies in growth. Skeletal defects included hypoplasia of digital phalanges and nails and shortened wings.

Abnormalities, Drug-Induced↗
PubMed1989

Synthesis of site-specific methotrexate-IgG conjugates. Comparison of stability and antitumor activity with active-ester-based conjugates.

With a view to increasing drug incorporation without loss of antibody activity, tritium-labeled methotrexate (MTX) was covalently linked to a polyclonal rabbit IgG antibody against bovine serum albumin and a monoclonal mouse IgG antibody against human renal cancer (Dal K20) by a site-specific method based on hydrazone bond formation between MTX hydrazide and the aldehyde groups generated by periodate oxidation of carbohydrate moieties in IgG (which are uncommon in the antigen-binding region). These conjugates were compared with the corresponding non-site-specific MTX-IgG conjugates produced by the N-hydroxysuccinimide active-ester method with regard to synthesis, stability, retention of antibody activity, inhibition of the target enzyme dihydrofolate reductase and antitumor effect. Incorporation levels achieved with the hydrazide method were no greater than with the active-ester method, typically 6-7 mol MTX/mol IgG. Approximately the same dihydrofolate-reductase-inhibitory capacity was observed for MTX bound by either method. Hydrazide conjugates lost bound drug more rapidly than active-ester conjugates on freezing and thawing, on incubation at 37 degrees C and 51 degrees C, and in the presence of serum or rat liver homogenates. Exposure to rat liver homogenates at 37 degrees C, pH 4.6, for 24 h led to the loss of 50%-60% of the bound drug from hydrazide conjugates compared to 20%-30% from the active ester conjugates. Bio-Gel P-2 chromatography of low-molecular-mass fractions, obtained after exposure of each of the conjugates to liver homogenates, revealed the presence of a compound that had the same elution volume and RF on thin-layer chromatography as free MTX. Enzyme-linked immunosorbent assay showed loss of antibody activity of both types of conjugates at 51 degrees C and on freezing and thawing. In a clonogenic assay, the active-ester conjugate of Dal K20 appeared to be equally effective or slightly better as a tumor inhibitor than the corresponding hydrazide conjugate. The hydrazide method may be useful in linking MTX to those monoclonal antibodies that tend to denature when subjected to the active-ester method of linkage.

Antibodies, Monoclonal↗
PubMed1989

Identification of a regulatory nifA type gene and physical mapping of cloned new nif regions of Azospirillum brasilense.

Three new Tn5-mutagenized nif genes of Azospirillum brasilense were characterized. The sizes of the restriction fragments and the restriction maps of the cloned nif DNA regions showed that these nif genes are distinct from those reported earlier, e.g. nifHDK, nifE, nifUS, fixABC. The Nif27 mutant was identified as a nifA type regulatory gene of A. brasilense (a) by genetic complementation with nifA of Klebsiella pneumoniae, (b) by the absence of nitrogenase iron protein in western protein blots and (c) by its inability to activate expression of a nifH-lacZ fusion. The growth characteristics of the three mutants showed that none of them is defective in general nitrogen regulatory (ntr) genes. Also, no homology was detected between the three nif DNA regions of the mutants, cloned in pMS188, pMS189 and pMS197, and the K. pneumoniae nif, glnA or ntr genes. In addition, the fixABC genes of Bradyrhizobium japonicum did not show any hybridization with the cloned Azospirillum genes. Unlike the situation in enteric bacteria, the nif genes in A. brasilense are scattered and span a region of about 65 kb.

Azospirillum brasilense↗
PubMed1989

Three-dimensional reconstruction of cardiac displacement patterns on the chest wall during the P, QRS and T-segments of the ECG by laser speckle interferometry.

A noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall. These displacements are then reconstructed in the form of three-dimensional plots, during the P, QRS and T-waves of the ECG. A comparison of these patterns shows that the mechanical activity of each region varies significantly during these phases of cardiac cycle. As these displacements depend on the clinical status of the heart, its use with a cardiac patient shows the functional changes of the affected regions in the form of alteration of these patterns.

Electrocardiography↗
PubMed1989

Influence of hypercholesterolemia on morphological and rheological characteristics of erythrocytes.

The changes in shape and rheological parameters of erythrocytes in cholesterol-fed rabbits (fed with normal diet plus 0.5% cholesterol for a duration of 1 year) and in vitro cholesterol enrichment of erythrocytes in cholesterol enriched plasma were studied. This process affects the shape of erythrocytes. In rabbits the actual shape change begins after 6 weeks of cholesterol feeding. The shape changes in rabbits and in vitro cholesterol-enrichment are similar. The extent of shape changes depends on the amount of cholesterol incorporated into the membrane. The rheological parameters such as blood viscosity, osmotic fragility and deformability are measured. The whole blood viscosity is increased and deformability decreased. The cells become osmotically more fragile in cholesterol-fed rabbits but are resistant to osmotic lysis in in vitro cholesterol enrichment. The altered lipid composition may be responsible for the observed changes in these parameters.

Animals↗
PubMed1989

Asymmetries in the perception of facial affect: is there an influence of reading habits?

Perceptions of happy facial affect from asymmetric composite faces presented in free vision were compared in four groups: left-to-right readers (Hindi), right-to-left readers (Arabic), left-to-right and right-to-left readers (Hindi/Urdu) and illiterates (Hindi/Urdu). Right- and left-handed users of Hindi and Urdu were studied. The analysis of asymmetry scores revealed a significant effect of Group, such that a left hemifield preference was present only in the left-to-right (Hindi) group. There were no reliable differences between right- and left-handers. Furthermore, the leftward bias was present in a significantly larger proportion of Hindi than Urdu or Arabic readers. These results are taken to reflect an interaction between a cerebral laterality effect and a directional scanning effect in facial affect judgment.

Adult↗
PubMed1989

Primary biodegradation of linear alkyltoluene and alkylbenzene sulfonates.

Studies on the primary biodegradation of linear dodecylbenzene sulfonate, linear dodecyltoluene sulfonate, linear C(10-14) benzene sulfonate, linear C(10-14) toluene sulfonate, commercial samples of linear C(10-14) benzene sulfonate and branched dodecylbenzene sulfonate (DDBS) were carried out using a microbial culture developed from garden soil. Results show that linear alkyl toluene (LAT) is as degradable as linear alkylbenzene (LAB) in 7 days. However, a slower rate of degradation was noted with LAT. Various distributions of the positional isomers of the phenyl ring in the alkane chain of C(10-14) LAB showed no change in the pattern of primary biodegradation.

Journal Article↗
PubMed1989

Contraceptive efficacy of norethindrone encapsulated in injectable biodegradable poly-dl-lactide-co-glycolide microspheres: phase II clinical study.

Contraceptive efficacy of injectable norethindrone (NET) microspheres of 90 day duration was evaluated for 6 months: nine women received two injections of 65 mg each and eight received two injections of 100 mg each with 90 days between each injection. Average serum NET levels were 5 to 9 ng/mL on the day after injection and subsequently remained at 1 to 3 ng/mL. With 65 and 100 mg doses, respectively, 36% and 25% of cycles had normal bleeding patterns, 36% and 48% were amenorrheic, and the remaining 28% and 27% had prolonged bleeding. Also, 56% and 40% of cycles showed increased spotting for the 65 mg and 100 mg dose, respectively. There was no incidence of pregnancy or serious side effects. The mean serum NET concentration returned to RIA nonspecific basal levels 100 days after the second injection. Women returned to ovulatory cycles between days 100 to 115 after the second injection.

Adult↗
PubMed1989

Inhibition of human renal cancer by methotrexate linked to a monoclonal antibody.

The monoclonal antibody DAL K29 against a human renal cell carcinoma associated cell surface antigen was covalently linked to the antifolate methotrexate with full retention of antibody reactivity and partial retention of drug activity. In a colony inhibition assay, antibody-conjugated methotrexate was 400% more potent in inhibiting the growth of the human kidney cancer line Caki-1 than equimolar amounts of the free drug. Comparable amounts of the antifolate linked to normal mouse IgG did not inhibit the growth of Caki-1 cells. Furthermore, the methotrexate-DAL K29 conjugate had no effect on the two nontarget human cell lines tested, melanoma M21 and B cell leukemia D10-1 cells, even when the conjugate contained amounts of methotrexate equivalent to the 50% inhibitory concentration of the free drug for the nontarget cell lines or an amount equivalent to the 50% inhibitory concentration of the conjugated drug for Caki-1 cells.

Antibodies, Monoclonal↗
PubMed1989

Synthesis of methotrexate-antibody conjugates by regiospecific coupling and assessment of drug and antitumor activities.

In order to increase the retention of drug activity, regiospecific coupling has been used to synthesize conjugates of methotrexate (MTX, 1) with normal rabbit IgG (NRG) and a mouse anti-human renal cancer monoclonal IgG (Dal K-20). MTX gamma-methyl ester (4) was produced either by selective esterification of MTX or by coupling of 4-amino-4-deoxy-N10-methylpteroic acid (2) with suitable glutamic acid derivatives. The MTX gamma-methyl ester (4) was then converted to the corresponding hydrazide 6. An amide-linked conjugate was formed when the MTX gamma-hydrazide (6) was converted to reactive acylating species 7 by using tert-butyl nitrite or trifluoroacetaldehyde, which were reacted with nucleophilic centers, presumably epsilon-amino groups, in native IgG. A hydrazone-linked conjugate was formed when MTX gamma-hydrazide (6) was reacted directly with IgG that had first been oxidized with periodate to form polyaldehyde IgG. The regiospecifically synthesized conjugates were somewhat more effective inhibitors in vitro of dihydrofolate reductase and of colony formation by human renal cancer (Caki-1) cells than were control nonregiospecific conjugates.

Antibodies, Monoclonal↗
PubMed1989

Actinomycetic corneal ulcer.

A rare case of keratoactinomycosis developing in the absence of any known ocular trauma is described. It showed a dramatic response to penicillin therapy. Steroids should be cautiously used in the presence of active corneal disease. This case highlights the importance of repeated examination of corneal scrapings.

Actinomyces↗
PubMed1989

Human immunodeficiency virus 1 tat protein binds trans-activation-responsive region (TAR) RNA in vitro.

tat, the trans-activator protein for human immunodeficiency virus 1 (HIV-1), has been expressed in Escherichia coli from synthetic genes. Purified tat binds specifically to HIV-1 trans-activation-responsive region (TAR) RNA in gel-retardation, filter-binding, and immunoprecipitation assays. tat does not bind detectably to antisense TAR RNA sequences, cellular mRNA sequences, variant TAR RNA sequences with altered stem-loop structures, or TAR DNA.

Base Sequence↗