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R Dixit

Publications and source records attributed to R Dixit.

At least 55 records · Page 3Linked to original sources
PubMed1986

Benzo(alpha)pyrene metabolism and DNA-binding in cultured explants of human bronchus and in monolayer cultures of human bronchial epithelial cells treated with ellagic acid.

Ellagic acid, a plant phenolic compound present in certain foods eaten by humans, has been reported to possess antimutagenic and anticarcinogenic properties. To evaluate the potential anticarcinogenic effect of ellagic acid in humans, we investigated the effect of nontoxic concentrations of ellagic acid on the metabolism of benzo(alpha)pyrene and binding of benzo(alpha)pyrene metabolites to DNA in cultured explants of human bronchus and in human bronchial epithelial cell cultures. Ellagic acid at concentrations of 10, 25, or 50 microM did not significantly alter the metabolism of benzo(alpha)pyrene in the bronchial explant cultures and in only one of four bronchial cell cultures. However, binding of metabolites of benzo(alpha)pyrene to DNA was inhibited in all explant and cell cultures of human bronchus by 26 to 77%. These results support the work of other investigators and suggest that ellagic acid may be an inhibitor of polycyclic aromatic hydrocarbon-induced carcinogenesis in humans.

Adult↗
PubMed1985

Isolation and partial characterization of a novel basement membrane collagen.

A guanidine-HCl extraction of lens capsule basement membrane dissolves collagenous material. This material was fractionated on an Agarose A-5M column. Fractions 1, 2 and 3 were further purified and partially characterized immunochemically and by amino acid analysis. Fraction 3 has a molecular weight of 55,000 when compared with collagen type I standard. The CNBr peptide pattern and composition of fraction 3 are different from those of alpha 1 (IV) 95K and alpha 2 (IV) 95K chains. The results described suggest the presence of a new chain in lens capsule basement membrane.

Amino Acids↗
PubMed1985

In vivo and in vitro metabolism of 2,4-dinitrotoluene in strain A mice.

The elimination and metabolism of a single dose (100 mg/kg) of 2,4-dinitrotoluene (2,4-DNT) in A/J mice were examined. After intraperitoneal administration, elimination was rapid, with 70% of the dose appearing in the urine within 4 hr. Four hours after oral administration, only 28.5% of the dose was excreted in the urine, which increased to 66% after 8 hr. Elimination via the feces was minimal (less than 2.1% of the dose) in both cases. From 0.5 to 4 hr after intraperitoneal administration, 3.6 to 8.8% of the urinary metabolites was unconjugated while 2.4 to 8.8% was present in the glucuronide fraction. After oral administration these amounts were 5.5 to 6.8% and 20.5 to 28.2% respectively. After both intraperitoneal and oral administration, no unchanged 2,4-DNT could be detected in the urine, and 2,4-dinitrobenzyl alcohol (2,4-DNBAlc) represented the most abundant identifiable neutral metabolite. Small amounts of 2,4-diaminotoluene, 2-amino-4-nitrobenzyl alcohol, 2-(N-acetyl)amino-4-nitrotoluene, 4-amino-2-nitrotoluene (4A2NT), and 2-amino-4-nitrotoluene (2A4NT) were also present. In almost all cases the largest proportion of metabolites represented unknowns, some of which exhibited the chromatographic properties of carboxylic acid metabolites. Metabolism of 2,4-DNT by liver and lung microsomes yielded mainly 2,4-DNBAlc with lower amounts of 4A2NT and 2A4NT, and their formation was dependent on the presence of oxygen and NADPH. Pretreatment of the animals with 2,3,7,8-tetrachlorodibenzo-p-dioxin resulted in increased yields of all three metabolites. Aerobic metabolism of 2,4-DNT by explants of the small intestine, large intestine, or by cecal contents yielded 2,4-DNBAlc, 2A4NT, 4A2NT and 4-(N-acetyl)amino-2-nitrotoluene (4Ac2NT). The proportion of reduced metabolites (2A4NT, 4A2NT, and 4Ac2NT) was much higher in these systems than with liver or lung microsomes and their formation by small intestine and cecal contents was enhanced several-fold under anaerobic conditions, while that of 2,4-DNBAlc was abolished. It is concluded that 2,4-DNT metabolism in the A/J mouse is rapid and complete and that the major neutral urinary metabolite is 2,4-DNBAlc. Minor amounts of reduced or partially reduced products appear to be formed mainly in the intestine, with a major role by its microflora.

Acetylation↗
PubMed1985

The effect of ellagic acid on the uptake, persistence, metabolism and DNA-binding of benzo[a]pyrene in cultured explants of strain A/J mouse lung.

Ellagic acid (EA), a plant phenol found in a variety of fruits and vegetables normally consumed by humans, inhibited the metabolism of benzo[a]pyrene (B[a]P) and covalent binding of B[a]P metabolites to DNA in cultured lung explants from strain A/J mice. Explants were incubated in medium containing EA at concentrations of 10 - 100 microM for 16 h followed by the addition of 1 microM [3H]B[a]P for 24 h. Culture medium was extracted and analyzed by high-performance liquid chromatography. DNA from the explants was extracted, purified and quantitated to determine B[a]P metabolite binding to DNA. EA at concentrations of 10, 25, 50, 100 microM inhibited the metabolism of B[a]P in lung explants by 24-47% and DNA-binding of B[a] metabolites by 36-71%. Analysis of total lipids and trichloroacetic acid insoluble fractions of homogenized lung explants showed two to three times more radioactivity in EA-treated cultures even though EA did not affect the uptake of B[a]P. Explants maintained for four days after the removal of EA and [3H]B[a]P from the culture medium exhibited significant persistence of B[a]P and B[a]P metabolites associated with the total lipid and TCA insoluble fractions and in B[a]P metabolites bound to DNA. H.p.l.c. analysis of the total lipids extracted from homogenized lung explants showed that during the first 3 days of incubation most of the radioactivity in the EA-treated cultures was unmetabolized B[a]P while that in the control cultures existed as metabolites of B[a]P. The inhibition of metabolism of B[a]P and the consistently lower B[a]P-DNA binding in EA-treated mouse lung explants support the role of EA as a naturally occurring inhibitor of B[a]P-induced carcinogenesis.

Animals↗
PubMed1985

Interaction of certain metal ions with aryl hydrocarbon hydroxylase of rat lung microsomes.

The effect of varying concentrations of cadmium, copper, zinc, and selenite on the activity of aryl hydrocarbon hydroxylase (AHH) of rat lungs was studied in vitro. All the metals resulted in a strong inhibition of enzyme activity. Copper and zinc were more inhibitory to rat lung AHH than cadmium and selenite. There was an additive inhibition of AHH activity when copper or zinc was added in the presence of cadmium. EDTA or glutathione exerted a protective effect on cadmium-induced inhibition of AHH activity. Prior incubation of the microsomes with N-ethylmaleimide, a thiol-blocking agent, had no effect on the inhibition of AHH activity caused by cadmium. Addition of cadmium along with zinc-thionein resulted in increased inhibition of rat lung AHH.

Animals↗
PubMed1985

Role of active oxygen species in the photodestruction of microsomal cytochrome P-450 and associated monooxygenases by hematoporphyrin derivative in rats.

The cytochrome P-450 in hepatic microsomes prepared from rats pretreated with hematoporphyrin derivative was shown to be rapidly destroyed in the presence of long-wave ultraviolet light. The photocatalytic destruction of the heme-protein was dependent on both the dose of ultraviolet light and of hematoporphyrin derivative administered to the animals. The destructive reaction was accompanied by increased formation of cytochrome P-420, loss of microsomal heme content, and diminished catalytic activity of cytochrome P-450-dependent monooxygenases such as aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase. The specificity of the effect on cytochrome P-450 was confirmed by the observation that other heme-containing moieties such as myoglobin and cytochrome c were not susceptible to photocatalytic destruction. The destruction of cytochrome P-450 was a photodynamic process requiring oxygen since quenchers of singlet oxygen, including 2,5-dimethylfuran, histidine, and beta-carotene, each substantially diminished the reaction. Scavengers of superoxide anion such as superoxide dismutase and of H2O2 such as catalase did not protect against photodestruction of cytochrome P-450, whereas inhibitors of the hydroxyl radical, including benzoate, mannitol, and ethyl alcohol, did afford protection. These results indicate that lipid-rich microsomal membranes and the heme-protein cytochrome P-450 embedded therein are potential targets of injury in cells exposed to hematoporphyrin derivative photosensitization.

Animals↗
PubMed1985

Inhibition of benzo(a)pyrene and benzo(a)pyrene-trans-7,8-diol metabolism and DNA binding in mouse lung explants by ellagic acid.

The effect of ellagic acid, a naturally occurring plant phenol, on the binding to DNA and metabolism of benzo(a)pyrene (BP) and trans-7,8-dihydro-7,8-dihydroxybenzo(a)pyrene (BP 7,8-DHD) in cultured explants of strain A mouse lung was investigated. The explants were cultured in a rocking organ culture chamber for 16 h in the presence or absence of 10, 25, 50, and 100 microM ellagic acid. These concentrations of ellagic acid were nontoxic as determined by biochemical and histological methods. The ellagic acid was then removed from the cultures, and the explants were incubated with either 1 microM [3H]BP or [3H]BP 7,8-DHD for 24 h. Explant DNA was isolated using hydroxylapatite chromatography, and the BP metabolites in the medium were analyzed by high-pressure liquid chromatography. Ellagic acid (50 microM) inhibited the binding of BP and BP 7,8-DHD to lung DNA by 46 to 50% and 60 to 70%, respectively. High-pressure liquid chromatography analysis showed that ellagic acid (100 microM) inhibited the metabolism of BP by 20 to 40% and of BP 7,8-DHD by 20%, as indicated by the increased amounts of unmetabolized substrates and decreased amounts of metabolites in the medium. The major BP:DNA adduct in the explants was 7R-N2-[10 beta-[7 beta, 8 beta, 9 alpha-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]yl: deoxyguanosine, and its formation was reduced by 60 to 65% in the presence of 100 microM ellagic acid. These data suggest that the reduction of BP and BP 7,8-DHD metabolite binding to DNA by ellagic acid may have been due to inhibition of the formation and/or removal of BP 7,8-diol-9,10-epoxide prior to its binding to DNA.

Animals↗
PubMed1984

Enhancement of bleomycin-mediated DNA damage by epidermal microsomal enzymes.

The role of epidermal microsomal enzymes in catalyzing bleomycin-mediated chain breakage in calf-thymus DNA and in DNA isolated from neonatal rat epidermis was studied. Aerobic incubation of bleomycin with epidermal microsomes, epidermal or calf-thymus DNA and NADPH caused substantial chain breakage of the DNA which was dependent upon concentrations of drug, microsomal protein and NADPH. The reactive oxygen scavenger superoxide dismutase, the metal chelator EDTA, and cytochrome c each inhibited the enzyme-mediated chain breakage reaction. Scavengers of hydrogen peroxide and hydroxyl radicals, including catalase and benzoate and inhibitors of microsomal cytochrome P-450-dependent monooxygenases such as 1-benzylimidazole, metyrapone and alpha-naphthoflavone, had no inhibitory effects on bleomycin-mediated DNA chain breakage. In contrast, ascorbic acid significantly enhanced DNA damage by bleomycin. These studies indicate that mammalian epidermis possesses membrane-bound enzyme activity capable of enhancing bleomycin-mediated chain breakage of DNA and that oxidation/reduction of adventitious iron and generation of reactive oxygen participate in the reaction. These responses in the epidermis could directly relate to the mechanism of action of intralesional injections of bleomycin which are used quite effectively in the management of recalcitrant human warts. Either epidermal or wart virus DNA or both could be targets for this pharmacologic effect of the drug which is augmented by epidermal microsomal enzymes.

Animals↗
PubMed1984

Interaction of acrylamide with glutathione in rat erythrocytes.

Evidence is presented for an enzyme-catalyzed conjugation of acrylamide (ACR) in rat erythrocytes. Daily exposure of rats to ACR for a period of 7, 14 and 21 days resulted in a time-dependent decrease in glutathione content. In vitro incubation of ACR with rat erythrocytes suspension caused a concentration-dependent decrease in glutathione levels. Red blood cell (RBC) enzyme-catalyzed conjugation of ACR with glutathione increased with protein concentration and was dependent on pH and time of incubation. Glutathione-S-transferase (GST) activity using acrylamide and 1-chloro 2,4-dinitrobenzene (CDNB) as substrates followed the order: liver greater than kidney greater than brain greater than erythrocytes. Glutathione peroxidase activity of RBC's was inhibited by the in vitro addition of ACR to erythrocytes. These results suggest that rat erythrocytes are equipped with the mechanism which can inactivate toxic electrophilic chemicals, such as acrylamide.

Acrylamide↗
PubMed1983

Studies on the role of reactive oxygen species in mediating lipid peroxide formation in epidermal microsomes of rat skin.

The role of superoxide, hydrogen peroxide, and singlet oxygen in mediating nonenzymic and NADPH-supported enzymic lipid peroxidation in skin microsomes was investigated. Incubation of skin microsomes with NADPH and/or Fe+3-ADP or ascorbate resulted in the formation of lipid peroxides. The epidermis was the major target site for microsomal lipid peroxide formation in skin. Enzymic peroxidation of epidermal microsomes required NADPH and was oxygen-dependent. Addition of the nonenzymic catalysts, Fe+3 and ADP, to the enzymic peroxidation system had an additive effect on the generation of lipid peroxide in epidermal microsomes. Epidermal microsomal lipid peroxidation was inhibited by singlet oxygen quenchers such as dimethylfuran, histidine, and beta-carotene. Hydroxyl ion scavengers such as mannitol, benzoate, or ethyl alcohol and the enzymic scavenger of superoxide, superoxide dismutase, were all ineffective in this respect. Addition of EDTA, Mn+2, cytochrome c+3, and catalase to the NADPH-supported enzymic peroxidation system resulted in strong inhibition of lipid peroxide formation in skin. Glutathione or epidermal cytosol added alone or in combination to the NADPH-supported incubation system enhanced peroxidation of microsomal lipids. Vitamin E (alpha-tocopherol) inhibited lipid peroxidation. These results indicate that singlet oxygen may mediate lipid peroxide formation in epidermal microsomes.

Adenosine Diphosphate↗
PubMed1982

Ligand binding specificity of a rabbit alveolar macrophage receptor for C3b.

We have recently reported the isolation from rabbit alveolar macrophages of a receptor which retained its ligand-binding activity for the third component of complement (C3) and for its major proteolytic derived activation fragment (C3b). The isolated receptor demonstrated a greater ability to bind C3b than an equimolar amount of C3. C3b differs from C3 in at least two ways: it is a proteolytic cleavage product of C3 and it lacks the internal thiolester bond of C3. We have analyzed the binding ability to isolated receptor to various C3 and C3b analogs and we demonstrate that the specificity of the C3b-C3b receptor interaction depends upon the lysis of the C3 thiolester bond and accompanying conformational change rather than upon proteolytic cleavage of the C3 molecule. Minimal, if any, binding of C3 with an intact thiolester bond to the isolated receptor was demonstrable.

Animals↗
PubMed1982

Depletion of glutathione content and inhibition of glutathione-S-transferase and aryl hydrocarbon hydroxylase activity of rat brain following exposure to styrene.

Dose dependent effects of styrene on cellular glutathione content and activity of cytosolic glutathione-S-transferase and microsomal aryl hydrocarbon hydroxylase of rat brain was investigated. A significant inhibition of aryl hydrocarbon hydroxylase and glutathione-S-transferase activity followed by depletion of glutathione content, was observed only at higher doses (450 and 900 mg/kg). Results suggest that exposure of styrene to rats can affect the biotransformation capacity of brain dependent on glutathione content and the activities of aryl hydrocarbon hydroxylase and glutathione-S-transferase.

Animals↗