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Biomedical subjects

M Das

Publications and source records attributed to M Das.

At least 181 records · Page 10Linked to original sources
PubMed1988

Alpha 2-antagonistic effect of N-carbamoyl-2-(2,6-dichlorophenyl) acetamidine hydrochloride (LON-954).

The effect of N-carbamoyl-2-(2,6-dichlorophenyl) acetamidine hydrochloride (LON-954) on alpha 2-adrenoceptors was studied in in vivo and in vitro preparations. Like yohimbine, LON-954 antagonised the clonidine-induced inhibition of twitch responses in the Auerbach's plexus of guinea pig ileum and rat vas deferens preparations. It also reversed the anti-convulsant effect of clonidine on pentylenetetrazol (PTZ)-induced convulsions in the rat, a property shared by yohimbine. However LON-954 failed to prevent the hypothermic response to clonidine in mice. The dissimilarity in action of LON-954 and yohimbine on clonidine-induced hypothermia could be due to the fact that the anticlonidine effect of yohimbine on hypothermia is mediated through its antiserotonin action. The results indicate that LON-954 acts as an alpha 2-antagonist both centrally and peripherally.

Adrenergic alpha-Antagonists↗
PubMed1988

Biosynthesis and turnover of a 34-kDa protein growth factor in human cytotrophoblasts.

Recently we isolated a new protein growth factor of 34 kDa from synctial membranes of human placenta. In its polypeptide molecular mass, antigenic structure, receptor binding specificity and partial amino acid sequence, it is unlike several known growth factors, hormones and other proteins. Here we report studies on its biosynthesis and turnover in cultured cytotrophoblasts from term human placenta. Expression of the 34-kDa protein in these cells was studied by immunoprecipitation and Western blot analyses using a highly specific antibody. The experiments have produced the following results. a) Immunostaining and Western blot analyses have demonstrated the presence of immunoreactive 34-kDa protein in isolated cytotrophoblasts. The protein is present in both freshly isolated cells and in cells that have fused in culture to form multinuclear syncytiotrophoblasts. b) Trophoblastic biosynthesis of the protein has been demonstrated by in vitro translation of cellular mRNA and by metabolic labelling experiments with intact cells. c) Pulse-chase experiments show that biosynthesis of the protein does not involve any detectable precursors of higher or lower molecular mass. d) Studies on turnover indicate that the synthesized protein is unusually stable with a half-life of 50-70 h.

Cells, Cultured↗
PubMed1988

Epidermal growth factor-induced stimulation of epidermal growth factor-receptor synthesis in human cytotrophoblasts and A431 carcinoma cells.

Epidermal growth factor (EGF)-receptor is a transmembrane glycoprotein whose intracellular degradation is known to be enhanced by EGF. We tested whether the receptor is replenished during this process by an enhanced rate of synthesis. Human A431 epidermoid carcinoma cells and primary cultures of human placental cytotrophoblasts were used in these studies. Cells were labeled with [35S]methionine, and EGF-receptor biosynthesis was quantitated by immunoprecipitation using a monoclonal anti-EGF-receptor antibody. EGF stimulated receptor biosynthesis at concentrations of 0.1 to 1 nM. The effect was seen within 2 h of EGF addition. At high EGF concentrations the stimulatory effect was diminished. In contrast, the effect of EGF on receptor degradation in these cells was negligible at low nanomolar concentrations and was pronounced only at saturating concentrations (greater than or equal to 10 nM). These results show that occupation of the cell surface EGF-receptor by its ligand can lead to the production of more receptor protein, thus counterbalancing the negative effect on receptor degradation. At low nanomolar concentrations of EGF the stimulatory effect on receptor synthesis predominates over degradation, indicating a positive regulatory role of EGF in receptor action.

Carcinoma, Squamous Cell↗
PubMed1988

Biochemical toxicology of argemone alkaloids. III. Effect on lipid peroxidation in different subcellular fractions of the liver.

Consumption of edible oils contaminated with Argemone mexicana seed oil causes various toxic manifestations. In this investigation the in vivo effect of argemone oil on NADPH-dependent enzymatic and Fe2+-, Fe2+/ADP- or ascorbic acid-dependent non-enzymatic hepato-subcellular lipid peroxidation was studied. Parenteral administration of argemone oil (5 ml/kg body weight) daily for 3 days produced a significant increase in both non-enzymatic and NADPH-supported enzymatic lipid peroxidation in whole homogenate, mitochondria, and microsomes. Lipid peroxidation aided by various pro-oxidants, namely Fe2+, Fe2+/ADP and ascorbic acid also revealed a significant enhancement in the whole homogenate, mitochondria and microsomes of argemone oil-treated rats. Further, when compared with whole homogenate, the hepatic mitochondria and microsomes of either control or argemone oil-treated rats showed a 4- and 6-fold increase in non-enzymatic, and a 5- and 18-fold increase in NADPH-dependent enzymatic lipid peroxidation, respectively. Similarly, both mitochondrial and microsomal fractions showed a 5- and 7-fold increase in Fe2+-, and a 12- and 15-fold increase in either Fe2+/ADP- or ascorbic acid-aided lipid peroxidation, respectively. These results suggest that the hepatic microsomal as well as the mitochondrial membrane is vulnerable to the peroxidative attack of argemone oil and may be instrumental in leading to the hepatotoxicity symptoms noted in argemone poisoning victims.

Animals↗
PubMed1988

Cell- and tissue-specific expression of a 34,000-molecular-weight peptide growth factor in humans.

A 34,000-dalton peptide growth factor that we originally identified in human placental trophoblasts and in certain carcinomas was shown to be expressed in several normal human tissues. A highly specific antibody to the trophoblast-derived growth factor was used in an immunoperoxidase staining technique to identify the immunoreactive peptide in tissue sections. Immunoreactivity was seen in the adrenal cortex, Leydig cells of the testes, and follicular cells of the thyroid. In addition, strong staining was seen in the ducts and terminal ductules of the pancreas, in glandular epithelium of the prostate, in the chief cells of the stomach, and in the columnar epithelium of the trachea and bronchus of the lung. Certain tissues were negative for the peptide, including the adrenal medulla, liver, esophagus, small intestine, colon, bladder, lymph node, spleen, bone marrow, and thymus. Thus, the expression of the peptide depends on cell lineage and the state of differentiation; tissues of hematopoietic lineage are devoid of the 34,000-dalton peptide, whereas some of the major hormone-secreting tissues that are under pituitary control show the highest immunoreactivity.

Adult↗
PubMed1988

A phospholipid is the membrane-anchoring domain of a protein growth factor of molecular mass 34 kDa in placental trophoblasts.

Recently we isolated a protein growth factor of 34 kDa from trophoblastic membranes of human placenta. A fraction (approximately equal to 50%) of the membrane-associated 34-kDa protein is peripherally associated--i.e., it can be released by high salt treatment. The remainder shows the characteristics of an integral membrane protein--i.e., its release requires detergent treatment. Here we report studies on the structural basis for membrane anchorage of the protein. Phospholipase C was found to release an immunoreactive 34-kDa polypeptide from intact isolated cytotrophoblasts. Studies with isolated trophoblastic membranes showed that phospholipase C specifically released the salt-resistant fraction of the 34-kDa polypeptide. The polypeptide released by phospholipase C showed the same electrophoretic mobility in NaDodSO4/PAGE as the polypeptide prior to phospholipase C treatment. The identity of the released protein with the 34-kDa growth factor has been established by both immunologic and receptor-binding assays. Other studies show that there is biosynthetic incorporation of [3H]myristate into the 34-kDa protein. The myristate label is labile to phospholipase C treatment. These results suggest that some of the 34-kDa protein is anchored to the plasma membrane via a posttranslationally added phospholipid. This mode of anchorage has been observed for some other membrane proteins and raises interesting questions regarding the role of this novel linkage in the mitogenic function of the 34-kDa polypeptide.

Acylation↗
PubMed1988

Lipid antioxidant properties of quercetin in vitro.

The effect of quercetin on iron-catalyzed hepatic microsomal lipid peroxidation was investigated. Quercetin was shown to be a potent inhibitor of iron-induced lipid peroxidation with a I50 of 0.2 mM. The inhibitory effects of quercetin were dependent on incubation time, protein concentration and iron content in the incubation mixture. Since quercetin does not interact with malonyl-aldehyde it can be concluded that the inhibition of iron induced lipid peroxidation is due to lipid antioxidant property and this may serve as a model for the study by which "free" iron may initiate peroxidation in vivo.

Animals↗
PubMed1987

7-Ethoxyresorufin-O-deethylase activity in human hair roots: a potential marker for toxifying species of cytochrome P-450 isozymes.

Assay systems for the evaluation of carcinogen interaction with human tissues are essential for assessing cancer risk. Human hair roots (HHR) are a readily obtainable epithelial tissue source that have been employed for investigating inherited enzyme activities. In this study HHR were found to possess cytochrome P-450-dependent 7-ethoxyresorufin-O-deethylase (ERD) activity which measures cytochrome P-450 isoenzymes that are highly specific (in the order of greater than 95%) markers for the metabolic activation of many environmental carcinogenic substances such as the polycyclic aromatic hydrocarbons (PAHs). Topical application of PAHs (in liquor carbonis detergens) to the scalp of human volunteers was found to enhance the activity of this enzyme in freshly plucked hair roots. Oral and topical administration of ketoconazole to the same subjects resulted in an appreciable (up to 73%) inhibition of detectable enzyme activity. Our data suggest that measurement of ERD in HHR may be a useful marker for the study of toxifying species of cytochrome P-450 isozymes in human populations.

Carcinogens↗
PubMed1987

Induction of epidermal NAD(P)H:quinone reductase by chemical carcinogens: a possible mechanism for the detoxification.

NAD(P)H:quinone reductase, which plays an important role in the detoxification of carcinogenic metabolites as well as oxidative cellular damage, was found to be present in epidermal cytosol where its specific activity far exceeds (140-160%) the corresponding hepatic value. The effect of topical application of crude coal tar, 3-methylcholanthrene and polychlorinated biphenyl Aroclor 1254, on epidermal and hepatic cytosolic NAD(P)H:quinone reductase activities was investigated in neonatal rats, Sencar and athymic nude mice. A single topical application of each agent resulted in significant increases in epidermal (185%-389%) and hepatic (150-255%) enzyme activities. This inducible enzyme may play an important role in the detoxification of reactive quinone species during the course of malignant neoplasia and against oxidative cellular damage in skin.

Animals↗
PubMed1987

Presence of tumor-associated antigens in epidermal growth factor receptors from different human carcinomas.

The epidermal growth factor (EGF) receptor in two colon carcinoma lines and in one vulval carcinoma line tested contains carbohydrate determinants that are recognized by monoclonal antibodies to tumor-associated antigens. These antibodies are directed to sialylated Lea and to difucosylated structures of the Y type. Cell lines which react with these antibodies express these antigens on their surface glycolipids and glycoproteins, including the EGF receptor. These unusual carbohydrates are absent in EGF receptors from normal untransformed cells, and from tumor cells which do not express these specific antigens. Although EGF receptor represents only 0.1-2% of total plasma membrane proteins of antigen-positive carcinomas, it accounts for 20-80% of total protein-associated sialylated Lea/Y type of nonsecreted carbohydrates present in these cells. The results of cell-binding, immunoprecipitation, and Western blot analyses of the antigen-positive carcinomas indicate that sialylated Lea/Y type of antigenicity is intrinsic to the EGF receptors of these cells, and that the antigen is present in receptors from both over-expressing and normal-expressing carcinomas.

Animals↗
PubMed1987

Glutathione S-transferases of mouse lung. Selective binding of benzo[a]pyrene metabolites by the subunits which are preferentially induced by t-butylated hydroxyanisole.

Six isoenzymes of glutathione S-transferase (GST) present in mouse lung have been purified and characterized. GST I (pI 9.8) is a dimer of Mr-26,500 subunits and GST II is a heterodimer of Mr-26,500 and -22,000 subunits, and GST III (pI 7.9) and IV (pI 6.4) are dimers of Mr-24,500 subunits. GST V (pI 5.7) is a heterodimer of Mr-24,500 and -23,000 subunits, whereas GST VI (pI 4.9) is a dimer of Mr-23,000 subunits. Immunological studies indicate that the Mr-24,500 subunits present in GST III (pI 7.9) are distinct from those present in GST IV (pI 6.4) and V (pI 5.7). Structural and immunological studies provide evidence that at least five distinct types of subunits in their different binary combinations give rise to various GST isoenzymes of mouse lung. These isoenzymes express varying degrees of catalytic activities towards a wide range of electrophilic substrates including benzo[a]pyrene 7,8-oxide and benzo[a]pyrene 4,5-oxide. The dietary antioxidant t-butylated hydroxyanisole (BHA) preferentially induces GST II and III. Also, these two isoenzymes selectively bind benzo[a]pyrene (B[a]P) metabolites, indicating that they play an important physiological role in the detoxification of B[a]P metabolites. The preferential induction of the GST isoenzymes involved in the detoxification of activated B[a]P metabolites indicates that the anti-neoplastic activity of BHA against B[a]P-induced neoplasia in mouse lung [Wattenberg (1973) J. Natl. Cancer Inst. 50, 1541-1544] may be due to the enhanced detoxification of B[a]P metabolites.

Animals↗
PubMed1987

Binding of an antagonistic monoclonal antibody to an intact and fragmented EGF-receptor polypeptide.

A murine monoclonal antibody (No. 425) raised against human A431 carcinoma cells specifically immunoprecipitates the 170,000 molecular weight epidermal growth factor (EGF)-receptor from extracts of A431 cells as well as from extracts of human placenta and cultured fibroblasts, but does not recognize the murine receptor. Binding to the external domain of the human EGF-receptor was indicated by indirect immunofluorescent staining of fixed nonpermeable cells. The antibody binds to both glyco- and aglycoreceptor forms, indicating that the epitope is a part of the polypeptide chain. Binding of the antibody to the receptor is conformation dependent; i.e., denatured receptors lacking EGF-binding activity are not recognized by the antibody. The results of antibody binding studies indicate that the epitope is closely linked to the EGF binding active site, and is common to both high- and low-affinity EGF-receptors. Interaction of this epitope with the antibody inhibits EGF binding and bioactivity, and triggers receptor down-regulation, but does not generate EGFlike kinase-stimulatory or mitogenic responses either in vitro or in vivo. The antibody was tested for its ability to bind to domain-sized fragments of the 170-kDa EGF-receptor. It can recognize both the proteolytically generated 110-kDa EGF binding peptide, and a soluble 100-kDa EGF-receptor secreted by A431 cells. This indicates that the epitope recognized this antibody retains its conformation after proteolytic separation of the EGF binding domain from the rest of the receptor molecule.

Antibodies, Monoclonal↗
PubMed1987

Inhibition of epidermal xenobiotic metabolism in SENCAR mice by naturally occurring plant phenols.

Naturally occurring plant phenols such as tannic acid, quercetin, myricetin, and anthraflavic acid have been shown to inhibit the mutagenicity of several bay-region diol-epoxides of polycyclic aromatic hydrocarbons including benzo(a)pyrene (BP). The present study was designed to determine whether these plant phenols can alter epidermal cytochrome P-450-dependent monooxygenases in SENCAR mice. In vitro addition of these plant phenols to epidermal microsomal preparations inhibited aryl hydrocarbon hydroxylase (AHH) activity in a concentration-dependent manner. The 50% inhibitory concentrations for tannic acid, myricetin, quercetin, and anthraflavic acid ranged from 4.4 X 10(-5) M to 12.4 X 10(-5) M in microsomes prepared from control and 3-methylcholanthrene-pretreated animals. Of the plant phenols studied tannic acid was found to be the most potent inhibitor of epidermal AHH activity. Tannic acid, quercetin, myricetin, and anthraflavic acid exhibited a mixed type of inhibitory effect with Ki values of 81, 63, 135, and 165 microM, respectively. In vitro addition of these plant phenols (240 microM) to the incubation mixture prepared from control and 3-methylcholanthrene-treated animals resulted in varying degrees of inhibition of epidermal microsomal AHH (57-92%), ethoxycoumarin O-deethylase (19-58%), and ethoxyresorufin O-deethylase (33-85%) activities. High pressure liquid chromatographic analysis of the organic solvent-soluble metabolites of BP produced by epidermal microsomes indicated a substantial decrease in the formation of BP-diols (23-67%) and BP-phenols (29-57%) by each of the plant phenols. The formation of BP-7,8-diol was substantially inhibited (29-52%) by each of the plant phenols. Further in vivo studies showed that a single topical application of tannic acid, quercetin, and myricetin greatly diminished epidermal AHH (53-65%), ethoxycoumarin O-deethylase (30-68%), and ethoxyresorufin O-deethylase (66-97%) activities whereas anthraflavic acid was ineffective in this regard even when repeatedly applied. Our results indicate that plant phenols have substantial though variable inhibitory effects on epidermal monooxygenase activities and BP metabolism suggesting that these compounds may be capable of inhibiting the carcinogenic effects of polycyclic aromatic hydrocarbons in the skin.

7-Alkoxycoumarin O-Dealkylase↗