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M Das

Publications and source records attributed to M Das.

At least 163 records · Page 9Linked to original sources
PubMed1990

Regulation of stability and synthesis of EGF-receptor mRNAs encoding for intact and truncated receptor forms.

The EGF-receptor is a proto-oncogene encoded membrane protein related to the v-erb-B oncogene product of avian erythroblastosis virus. Here we have studied the expression and stability characteristics of two forms of receptor mRNA--a 5.6 kb form that encodes for the intact transmembrane 170 kDa receptor and a 3' deleted 2.6 kb form that encodes for a 100 kDa secreted EGF-receptor. In previous studies we showed that EGF increased the synthesis of its own receptor in human cytotrophoblasts and A431 cells. Now we show that EGF stimulates the transcription of the receptor gene and blocks the degradation of transcripts, and thus elevates the level of receptor mRNA in these cells. To test the role of prior protein synthesis in these phenomena, we examined the effect of cycloheximide, and found that this reagent, either alone or in combination with EGF, leads to an increase in the level of EGF-receptor mRNA. Increases were seen in both size classes of receptor mRNA. Further analysis showed that cycloheximide enhances both synthesis and stability of receptor mRNA. While the intrinsic stability of the 3'-truncated 2.6 kb mRNA is approximately 2-fold higher than that of the 5.6 kb species, it is enhanced by more than 10-fold in the presence of cycloheximide and EGF acting in a synergistic manner. The extent of stabilization was less for the larger mRNA form. The results suggest the involvement of ligand as well as labile proteins in the control of synthesis and stability of EGF-receptor mRNA, and imply the involvement of 3' located structural features in the control of receptor mRNA stability.

Blotting, Northern↗
PubMed1989

Biochemical toxicology of argemone oil. IV. Short-term oral feeding response in rats.

Consumption of edible oils contaminated with Argemone mexicana seed oil is known to cause various clinical manifestations. In the present study, the effect of dietary intake of argemone oil on histopathological changes, haematological indices and selected marker parameters of toxicity was investigated to observe the exact sites and mode of action of argemone oil in rats. Histopathological changes in the liver showed increased fibrosis, hyperplasia of bile ducts and congestion in a few portal tracts. Lungs of argemone oil-fed animals indicated congestion and thickening of interalveolar septa. Alveolar spaces were disorganised and irregular. Kidneys showed vascular and glomerular congestion and patchy tubular lesions. At 30 days only mild congestion was noted in the myocardium. Cardiac muscle fibres showed degenerative changes at 60 days which were more marked in the auricular wall. Haematological examination showed appearance of anaemia in experimental animals. Hepatic alkaline phosphatase, alanine transaminase and aspartate transaminase activities were inhibited by 30, 29 and 29% after 30 days of argemone intake along with concomitant enhancement in serum by 27, 29 and 66%, respectively. Liver showed decrease in glutathione (32-63%) content along with significant stimulation of lipid peroxidation (49-105%) in argemone-intoxicated animals. These results suggest that liver, lungs, heart and kidneys are the target tissues of argemone oil toxicity and that membrane destruction may be a possible mode of action.

Animals↗
PubMed1989

Ligand-induced dimerization of the platelet-derived growth factor receptor. Monomer-dimer interconversion occurs independent of receptor phosphorylation.

The platelet-derived growth factor (PDGF) receptor is a single membrane-spanning polypeptide of 180,000 daltons with a ligand-stimulatable tyrosine kinase site. We have investigated changes in the structure and association state of the receptor that are induced by ligand binding, but which precede autophosphorylation. Chemical cross-linking of PDGF-bound 32P-labeled receptor and 125I-PDGF-labeled receptor resulted in the generation of a radiolabeled cross-linked complex of 370-390 kDa. This band, as well as the 180-190-kDa PDGF receptor band, were recognized by a PDGF receptor-specific antipeptide antibody. The appearance of the 370-390-kDa band was PDGF-dependent and was seen irrespective of whether the receptor was membrane-bound, solubilized, or highly (approximately 90%) purified. Sedimentation analysis of the 125I-PDGF cross-linked receptor showed that both 180-190- and 370-390-kDa labeled species sedimented as a single peak at about 11.5 S, a position expected of a receptor dimer, demonstrating that the liganded receptor exists essentially as a dimer. In contrast, unliganded receptors sedimented as a single species at 7 S, a position consistent with a monomeric structure. The monomer-dimer interconversion was absolutely ligand-dependent and occurred independent of autophosphorylation. These results demonstrate and intimate correlation between PDGF binding and inter-receptor bond formation, and raise the possibility that the phenomenon may be causally linked to the process of kinase activation.

Affinity Labels↗
PubMed1989

Aberrant postendocytotic fate of a 34-kDa molecular mass growth factor from human trophoblasts.

A 34-kDa growth factor expressed by trophoblasts and certain carcinomas binds to target fibroblastic cells through specific high-affinity receptors. Here we report studies on the cellular routing behavior of the receptor-bound 34-kDa protein. Internalization was visualized by using lissamine rhodamine-conjugated 34-kDa protein and was quantified by analyzing the acid dissociability of cell-bound radioiodinated protein after incubation at 37 degrees C. The protein was found to be rapidly internalized in a temperature-sensitive manner. However, in contrast with other protein ligands, the 34-kDa protein was not rapidly degraded. The extent of ligand degradation was small as quantified by gel filtration analysis. Studies on the receptor showed that there was an atypical up-regulation, i.e., increase in surface receptors in response to ligand binding at 37 degrees C. The up-regulation was partially blocked by cycloheximide, an inhibitor of protein biosynthesis, but not by known inhibitors of receptor recycling such as monensin, chloroquine, and methylamine, suggesting that enhanced receptor biosynthesis may be responsible for the process. These studies indicate that the cellular routing and receptor regulatory characteristics of the internalized 34-kDa growth factor are different from those of most growth factor ligands and imply the involvement of receptor up-regulation in signal transduction.

Cells, Cultured↗
PubMed1989

Protection against chemically induced skin tumorigenesis in SENCAR mice by tannic acid.

Tannic acid, a naturally occurring dietary polyphenol, was evaluated as a possible anticarcinogen in an initiation-and-promotion skin tumorigenesis protocol. In the 2-stage tumor protocol in SENCAR mice, using DMBA, BP and MNU as the initiating agents followed by twice-weekly applications of TPA as tumor promotor, tannic acid was found to be an effective inhibitor of tumor formation whether the tumor data are considered as cumulative number of tumors, percentage of mice with tumors or tumors/mouse. After 9 weeks of TPA application, the number of tumors/mouse in the groups receiving DMBA, BP and MNU were 32.10 +/- 3.18, 3.70 +/- 0.55 and 2.00 +/- 0.53, respectively, whereas the corresponding numbers in the DMBA, BP and MNU groups receiving prior applications of tannic acid were 11.50 +/- 2.38, 0.35 +/- 0.15 and 0.35 +/- 0.13, respectively. These results suggest that tannic acid may prove useful in reducing the risk of chemically-induced skin tumorigenesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

5-Hydroxytryptamine in the phrenic nerve diaphragm: evidence for its existence and release.

Evidence is presented for the existence of 5-hydroxytryptamine (5-HT) within the phrenic nerve of the rat and its release following electrical stimulation. Contents of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the phrenic nerve and the indoleamine released into the bathing fluid were estimated fluorimetrically after isolation on Sephadex G-10 and/or solvent-solvent extraction. Bioassays of 5-HT were done on rat fundus strip. The phrenic nerve and the end-plate zone contains high levels of 5-HT (1.9 micrograms/g wet weight) and 5-HIAA (1.5 micrograms/g wet weight). The resting release of around 1 ng 5-HT/diaphragm/min was enhanced by 50% (1.5 ng 5-HT/diaphragm/min) upon supramaximal (2-4 V) electrical stimulation of 5 Hz. Phrenic nerve diaphragm prepared from the denervated and p-chlorophenylalanine (300 mg/kg/day i.p. for 3 days) treated rats failed to release 5-HT confirming the neuronal origin and the identity of the indoleamine respectively. Furthermore, methysergide, an antagonist of 5-HT in rat fundus strip, blocked the response obtained by the sample on it. A modulatory role of 5-HT in the phrenic nerve diaphragm of the rat is envisaged from the present study.

Animals↗
PubMed1989

Characterization of cerebral 7-ethoxycoumarin-O-deethylase: evidence for multiplicity of cytochrome P450 in brain.

Characterization of 7-ECOD regulated by a number of cytochrome P450 species in liver has been undertaken in brain to understand whether it can metabolize a wide variety of substrates. Maximum activity of the enzyme was recorded when 0.8 to 2.0 mg of brain microsomal protein was added to the assay mixture at pH 7.4 and incubated for 30 min. The enzyme activity was found to be localized in the microsomal fraction with the maximum activity being in the olfactory lobes and the minimum in the pons medulla region. Kinetic studies revealed that rat brain microsomes exhibited a monophasic pattern of enzyme activity with a Km value of 2 mM. Rats pretreated with phenobarbital exhibited no change in enzyme activity whereas 3-methylcholanthrene preferentially stimulated enzyme activity (two- to threefold). The differential induction of enzyme activity after MC pretreatment and the differential response of alpha-naphthoflavone and metyrapone in vitro on 7-ECOD activity in control and MC-induced microsomes of rats, mice, guinea pigs, and rabbits do suggest the possibility of the presence of multiple forms of cytochrome P450 in the brain. Significant age, sex, and species-related differences observed in the activity of ECOD have also indicated that different forms of cytochrome P450 may be regulating the enzyme activity in the brain.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1989

Benzo(a)pyrene metabolism, DNA-binding and UV-induced repair of DNA damage in cultured skin fibroblasts from a patient with unilateral multiple basal cell carcinoma.

The metabolism of benzo(a)pyrene (BP), a ubiquitous environmental carcinogen, and its subsequent binding to DNA, and the repair of UV-induced DNA damage were studied in fibroblasts cultured from the skin of a 61-year-old male who had multiple BCC (greater than 100) on his left upper trunk. Biopsies were obtained and fibroblasts cultured from clinically normal tumour-free skin adjacent to tumour-bearing sites (TBS) and from visibly uninvolved normal skin (UNS) at distant sites. The cultured cells were incubated with [3H]-BP for 24 h and BP metabolism was assessed by HPLC and the formation of BP-diols, quinones and phenols verified. Total BP metabolism was 45% lower in TBS fibroblasts than in UNS fibroblasts. The formation of BP-7,8-diol, the precursor of the carcinogenic end product of BP metabolism, was 53% lower in TBS cells than in UNS cells. Pretreatment of UNS cells with benz(a)anthracene (BA) (x 10(-4) M) did not significantly affect BP metabolite formation whereas BA-treatment of TBS cells resulted in 55% and 76% increases in total BP metabolism and BP-7,8-diol formation, respectively. Treatment of TBS cells with BA also caused a substantial increase (95%) in BP-DNA adduct formation. Whereas DNA-binding in UNS cells was unaffected by this treatment. In response to irradiation with 2J/m2 UVC, total DNA repair was similar in both cell types; on alkaline elution it appeared that the TBS cells were more efficient in repairing UV-induced DNA strand breaks. These results suggest that BP metabolism and repair of DNA are altered in TBS cells and that patients with this type of metabolic profile may be at higher risk of the development of cutaneous neoplasms. It is also possible that fibroblasts from tumour bearing skin undergo some as yet unexplained alteration in carcinogen metabolism as a consequence of the induction of neoplasia.

Benz(a)Anthracenes↗
PubMed1989

Inhibition of tyrosine kinase activity of the epidermal growth factor (EGF) receptor by a truncated receptor form that binds to EGF: role for interreceptor interaction in kinase regulation.

The tyrosine kinase activity of the epidermal growth factor (EGF) receptor is regulated by a truncated receptor of 100 kilodaltons (kDa) that contains the EGF-binding site but not the kinase domain. The inhibition of kinase is not due to competition for available EGF or for the kinase substrate-binding site. Chemical cross-linking studies suggest that the 100-kDa receptor may form a heterodimer with the intact EGF receptor. Structurally related receptor kinases, such as the platelet-derived growth factor receptor, the insulin receptor, and the Neu receptor, were not inhibited by the 100-kDa receptor. The results indicate that (i) the inhibition was specific for the EGF receptor, (ii) the kinase domain had little or no role in determining target specificity, and (iii) the regulation of kinase may be due to a specific interaction of the 100-kDa receptor with the ligand-binding domain of the EGF receptor kinase.

Antibody Specificity↗
PubMed1989

Hepatic microsomal metabolism of leukotriene B4 in rats: biochemical characterization, effect of inducers, and age- and sex-dependent differences.

1. The cytochrome P-450-dependent metabolism of leukotriene B4 (LTB4) by rat hepatic microsomes was characterized. Hepatic microsomes were found to metabolize LTB4 to 20-hydroxy-LTB4 and 20-carboxy:LTB4. The rate of formation of 20-hydroxy-LTB4 (14.6 pmol/min per mg protein) was 5.8-fold higher than that of 20-carboxy-LTB4 (2.5 pmol/min per mg protein). 2. LTB4 omega-hydroxylase activity required NADPH and oxygen indicating that the reaction is mediated by a mono-oxygenase system. The omega-hydroxylase activity was optimal at pH 7.4 and product formation was linear with respect to time of incubation and protein concentration. The reaction was significantly inhibited by carbon monoxide (89%), SKF 525-A (1 mM), and metyrapone (0.1 mM) whereas alpha-naphthoflavone had only marginal inhibitory effects. The apparent Km and Vmax of LTB4 omega-hydroxylase were 4 microM and 19.6 pmol/min per mg protein, respectively. 3. Ontogenic studies revealed that LTB4 omega-hydroxylase activity was low in 4-day-old rats and that there was a steady increase in enzyme activity as the animal matured. 4. Phenobarbital, 3-methylcholanthrene or Aroclor 1254 treatment of rats did not induce LTB4 omega-hydroxylase activity whereas clofibrate resulted in 61% induction in enzyme activity. No significant sex-dependent differences were observed. 5. It is concluded that hepatic metabolism of LTB4 may afford an effective mechanism for limiting many of the pro-inflammatory effects of circulating leukotrienes.

Aging↗
PubMed1989

Dermal exposure to kerosene.

Young healthy albino male mice were subjected to repeated exposure to kerosene by wrapping each of their hind feet with a muslin cloth (1 x 10 cm) wetted with kerosene (0.1 ml). Exposure varied from 15 to 60 min/day for 7 consecutive days. Repeated exposure to kerosene produced histologic changes in the foot pad skin and popliteal lymph nodes of mice and systemic toxic manifestations such as variation in hematologic profile, significant decreases in relative weight of thymus, spleen and abdominal lymph nodes and altered histology. Three weeks of non-exposure rest indicated the reversible nature of kerosene-induced toxicity. Furthermore, observations made in 24 human subjects chronically exposed to kerosene in an automobile workshop revealed high incidence of oil acne and dermatitis of varying degrees. The study demonstrates a need for caution where ever prolonged dermal exposure to kerosene in occupational situations obtains.

Adult↗
PubMed1989

Physico-chemical aspects of solubility of myosin in aqueous media.

Solubility of fish (Labio rohita) myosin has been studied at varying temperatures in presence of various inorganic salts like NaCl, KCl, NaBr, Na2SO4, KI, and organic solutes like sucrose and urea. The effect of pH on the solubility has also been studied both in absence and presence of NaCl. Thermal denaturation temperatures of myosin in presence of NaCl, KCl, NaBr and Na2SO4 were found to be 40 degrees, 40 degrees, 45 degrees and 50 degrees C respectively. Thermodynamic parameters like changes in standard free energy (delta G degrees), enthalpy (delta H degrees) and entropy (delta S degrees) for precipitation of myosin from solution phase to gel phase have been evaluated and the physico-chemical aspects have been critically discussed. The average delta G degrees for gel formation varied only between -30 and -40 kJ/mole of myosin, although the nature of solutes, temperature and folding state of protein have been grossly altered. A compensation effect has also been exhibited from the linear plot of average values of delta H degrees against T delta S degrees for various solutes.

Animals↗
PubMed1989

Control of bancroftian filariasis by diethylcarbamazine medicated common salt in Karaikal, Pondicherry, India.

A trial of diethylcarbamazine (DEC) mixed in crystal common salt at a concentration of 0.15 to 0.2 per cent was carried out for 46 months (1982 to 1986) in Karaikal town and five commune panchayats of Pondicherry for control of bancroftian filariasis. Comparison of pre and post trial surveys showed 97.6 per cent reduction of microfilaria rate. No microfilaria or disease case was found in less than 5 years age group in the post trial survey. There was about 72 per cent reduction of disease rate. In the post trial substantial reduction of disease manifestation was found in 40 years and below age groups. Vector Culex quinquefasciatus density, filaria infection and infectivity rates were monitored only in Karaikal town. Infective vector mosquitoes were found in 1982 and 1983 only but afterwards no infective mosquito was encountered.

Adolescent↗
PubMed1989

Filariasis control in rural areas through detection and treatment with diethylcarbamazine.

A pilot study for control of bancroftian filariasis through detection and treatment of microfilaria (mf) carriers and filaria disease cases with Diethylcarbamazine (DEC) undertaken in the rural areas of Srikakulam and Vizianagaram of Andhra Pradesh showed that this chemotherapeutic method of control of filaria in rural areas is feasible and acceptable to society. During first round of detection and treatment 20,300 mf carriers (90.6 per cent of detected) and 6,588 disease persons (86 per cent of detected) in Srikakulam and 7,097 mf carriers (94.8 per cent of detected) and 1,436 disease persons (93.4 per cent of detected) in Vizianagaram were treated with DEC tablets. These areas were again surveyed after five years and detected cases were treated with DEC with coverage of treatment ranging from 82.3 per cent to 95 per cent for both mf & disease cases and decline in mf and disease rate was noted to be 52.4 per cent and 50.9 per cent respectively in Srikakulam and 42.2 per cent for mf rate in Vizianagaram. The mf reduction was appreciably high (50 per cent or more) in 11 PHCs of Srikakulam and 4 PHCs of Vizianagaram. The mf rate reduction was the highest in the age group of 1 to 4 year indicating that the transmission has been cut down significantly. The vector infection rate showed reduction by 50 per cent during second round of detection and treatment as compared to first round, indicating significant reduction in transmission potential.

Animals↗
PubMed1989

Benzanthrone: a new substrate for hepatic microsomal cytochrome P-450.

The metabolism of benzanthrone, a commonly used dy intermediate, by rat hepatic microsomes was investigated using thin layer chromatography (TLC) analysis. Incubation of benzanthrone with hepatic microsomes in the presence of NADPH generating system produced at least seven fluorescent metabolites on TLC plates. TLC spots numbered II, III, IV, V and VI were the major metabolites obtained from hepatic microsomes with the Rf values of 0.53, 0.45, 0.38, 0.33 and 0.26, respectively. Metabolites VII and VIII were faint bands with Rf values of 0.08 and 0.04, respectively. Preincubation of hepatic microsomes with either 1-benzyl-imidazole (10(-4)M) or SKF-525 A (10(-4)M) or metyrapone (10(-3)M) or flushing with carbon monoxide substantially inhibited the benzanthrone metabolism. alpha-Naphtho-flavone (10(-4)M) did not cause any change in hepatic microsomal metabolism of benzanthrone. Oral administration of benzanthrone to animals yielded at least six urinary metabolites. TLC spots numbered II, III, IV, V and VI in the urine were same as those of hepatic microsomal metabolites. However, one of the urinary metabolite numbered IX which stays at the origin of TLC plate with the Rf value of 0.05 may be a conjugate. Our results suggest that benzanthrone acts as a substrate for hepatic heme protein, cytochrome P-450 and that some of the metabolites are excreted in urine.

Animals↗
PubMed1988

Exceptional activity of tannic acid among naturally occurring plant phenols in protecting against 7,12-dimethylbenz(a)anthracene-, benzo(a)pyrene-, 3-methylcholanthrene-, and N-methyl-N-nitrosourea-induced skin tumorigenesis in mice.

Our recent studies have shown that naturally occurring dietary plant phenols such as tannic acid, quercetin, myricetin, and anthraflavic acid are capable of inhibiting polycyclic aromatic hydrocarbon (PAH) metabolism and subsequent PAH-DNA adduct formation in epidermis of SENCAR mice (M. Das, et al., Cancer Res., 47: 760-766, 1987, and 47: 767-773, 1987). In this study these plant phenols were tested for their effects against PAHs and N-methyl-N-nitrosourea-induced skin tumorigenesis in mice. Each plant phenol was evaluated as a possible anticarcinogen in an initiation and promotion and a complete skin tumorigenesis protocol. In the two-stage tumor protocol in SENCAR mice using 7,12-dimethylbenz(a)anthracene, benzo(a)pyrene, and N-methyl-N-nitrosourea as the initiating agent followed by twice weekly applications of 12-O-tetradecanoylphorbol-13-acetate as tumor promoter each plant phenol afforded significant protection against skin tumorigenicity. The protective effects were verified both by prolongation of latency period and by subsequent tumor development. In the complete carcinogenesis protocol in BALB/c mice using 3-methylcholanthrene as a tumorigen the applications of each of the plant phenols 30 min prior to each PAH application afforded significant protection by delaying the onset and the subsequent development of skin tumors. Our results suggest that these plant phenols have substantial though variable potential for modifying the risk of skin tumorigenicity induced by a wide variety of chemicals and of these tannic acid was shown to have maximal chemoprotective effects.

9,10-Dimethyl-1,2-benzanthracene↗