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J K Reddy

Publications and source records attributed to J K Reddy.

At least 109 records · Page 6Linked to original sources
PubMed1991

Alterations of pancreatic hepatocytes in rats exposed to carcinogens.

In this study, acute and chronic responses of pancreatic hepatocytes induced in F-344 rats by copper depletion-repletion protocol to certain hepatocarcinogens were examined. Administration of a single dose of tannic acid (subcutaneous), aflatoxin B1 (gavage), or lasiocarpine (intraperitoneally) caused characteristic nucleolar segregation in parenchymal cells of liver as well as in pancreatic hepatocytes. Chronic dietary administration of 2-acetylaminofluorene (0.025%) for 12 to 32 weeks led to the development of glutathione S-transferase-P-positive pancreatic hepatocytes in the pancreas. In addition, oval cell proliferation was observed in close association with pancreatic hepatocytes, but not in other areas of pancreas containing residual acinar cells. Oval cells in the pancreas and in the liver that developed in rats after chronic 2-acetylaminofluorene treatment and pancreatic duct cells stained positively with rat liver oval cell marker OV-6 antibodies by immunoperoxidase. These findings indicate that pancreatic hepatocytes respond to carcinogens in a fashion similar to parenchymal cells of liver.

2-Acetylaminofluorene↗
PubMed1990

Human urate oxidase gene: cloning and partial sequence analysis reveal a stop codon within the fifth exon.

Using the cDNA and selected genomic probes of rat urate oxidase, we have screened the human genomic library and isolated seven clones; one clone (clone 13) contained exonic regions which correspond to the exons 5, 6, and 7 of rat urate oxidase gene. The nucleotide sequence was determined for these three exons and exon/intron junctions, and compared with the sequence from the rat gene. A mutation resulting in a stop codon TGA was found in the fifth exon of the human urate oxidase gene. Sequence analysis of the polymerase chain reaction amplified DNA, corresponding to the fifth exon of urate oxidase from DNA samples from four different individuals, confirmed the same TGA stop codon in all. This single stop codon mutation and/or other mutation(s) in this gene may be responsible for the lack of urate oxidase activity in the human.

Amino Acid Sequence↗
PubMed1990

Peroxisome proliferator-induced alterations in the expression and modification of rat hepatocyte plasma membrane proteins.

Rats were fed the peroxisome proliferator ciprofibrate (0.025%), and the effects on the expression, modification, and localization of seven domain-specific integral proteins of the rat hepatocyte plasma membrane were assessed using a combination of immunoblotting, -precipitation, and -fluorescence. Ciprofibrate caused the down-regulation of five of the plasma membrane proteins (the epidermal growth factor receptor, the asialoglycoprotein receptor, HA 321, HA 4, and dipeptidylpeptidase IV) and induced the expression of a more basic, lower-Mr isoform of the basolateral plasma membrane protein CE 9. Pulse labeling, chemical deglycosylation, and 125I-wheat germ lectin blotting suggested that the ciprofibrate-induced isoform of CE 9 differed in the posttranslational modification of its oligosaccharides and contained more sialic acid. These changes in hepatocyte surface differentiation were first observed between Days 1 and 5 on the ciprofibrate-containing diet, coincident with other aspects of the pleiotropic response of the hepatocyte to peroxisome proliferators, e.g., the induction of the Mr 78,000 peroxisome proliferation-associated protein. The effects were reversed within 2-3 weeks upon removal of ciprofibrate. The three other peroxisome proliferators tested, di(2-ethylhexyl)phthalate, clofibrate, and Wy-14,643, were found to exert most of these same effects on the expression and modification of the hepatocyte plasma membrane proteins, but the compounds differed in relative potency. The ciprofibrate-induced decreases in the concentrations of the epidermal growth factor receptor, the asialoglycoprotein receptor, HA 321, and HA 4 were similar to the selective down-regulation of these proteins observed transiently during the period of hepatocyte proliferation following two-thirds hepatectomy. Other compounds frequently used in studies of liver enzyme induction and carcinogenesis, the antioxidants ethoxyquin and butylated hydroxyanisole and the liver tumor promoter phenobarbital, were not as effective as ciprofibrate or two-thirds hepatectomy at causing the down-regulation of these proteins. The induction of the lower-Mr isoform of the basolateral plasma membrane protein CE 9 was not observed following two-thirds hepatectomy or upon the feeding of the antioxidants or phenobarbital but was specific to the feeding of the peroxisome proliferators.

Antibodies, Monoclonal↗
PubMed1990

Identification of cytosolic peroxisome proliferator binding protein as a member of the heat shock protein HSP70 family.

Clofibrate and many of its structural analogues induce proliferation of peroxisomes in the hepatic parenchymal cells of rodents and certain nonrodent species including primates. This induction is tissue specific, occurring mainly in the liver parenchymal cells and to a lesser extent in the kidney cortical epithelium. The induction of peroxisomes is associated with a predictable pleiotropic response, characterized by hepatomegaly, and increased activities and mRNA levels of certain peroxisomal enzymes. Using affinity chromatography, we had previously isolated a protein that binds to clofibric acid. We now show that this protein is homologous with the heat shock protein HSP70 family by analysis of amino acid sequences of isolated peptides from trypsin-treated clofibric acid binding protein and by cross-reactivity with a monoclonal antibody raised against the conserved region of the 70-kDa heat shock proteins. The clofibric acid-Sepharose column could bind HSP70 proteins isolated from various species, which could then be eluted with either clofibric acid or ATP. Conversely, when a rat liver cytosol containing multiple members of the HSP70 family was passed through an ATP-agarose column, and eluted with clofibric acid, only P72 (HSC70) was eluted. These results suggest that clofibric acid, a peroxisome proliferator, preferentially interacts with P72 at or near the ATP binding site.

Amino Acid Sequence↗
PubMed1990

Coexpression of glutamine synthetase and carbamoylphosphate synthase I genes in pancreatic hepatocytes of rat.

In the mammalian liver the distribution of ammonia-detoxifying enzymes, glutamine synthetase (GS) and carbamoylphosphate synthase I (ammonia) (CPS-I), is mutually exclusive in that these enzymes are expressed in two distinct populations of hepatocytes that are zonally demarcated in the liver acinus. In the present study we examined the distribution of GS and CPS-I in pancreatic hepatocytes to ascertain if the expression of these two genes in these hepatocytes is also mutually exclusive. Multiple foci of hepatocytes showing no clear acinar organization develop in the adult rat pancreas as a result of a change in the differentiation commitment after dietary copper deficiency. Unlike liver, GS and CPS-I are detected by immunofluorescence in all pancreatic hepatocytes. In situ hybridization revealed that all pancreatic hepatocytes contain GS and CPS-I mRNAs. The sizes of these two mRNAs in pancreas with hepatocytes are similar to those of the liver. The concomitant expression of GS and CPS-I genes in pancreatic hepatocytes may be attributed, in part, to the absence of portal blood supply to the pancreas vis-à-vis the lack of hormonal/metabolic gradients as well as to possible matrix homogeneity in the pancreas.

Animals↗
PubMed1990

Androgen regulated expression of the alpha 2u-globulin gene in pancreatic hepatocytes of rat.

Under a copper-deficient regimen, pancreatic cells in the adult rat can be found to undergo differentiation into hepatocytes. Pancreatic hepatocytes induced in male and female rats were examined for the expression of the androgen-inducible hepatic protein, alpha 2u-globulin. Alpha 2u-Globulin protein was demonstrable by immunoperoxidase method in all the pancreatic hepatocytes of male rats. Northern blot analysis confirmed the presence of 1.3 kb alpha 2u-globulin mRNA transcript in the pancreas of male rats with hepatocytes. Orchiectomy resulted in marked decrease of alpha 2u-globulin protein and its mRNA. Administration of dihydrotestosterone to castrated rats resulted in increased levels of alpha 2u-globulin mRNA and the amount of alpha 2u-globulin protein in the pancreatic hepatocytes. Unlike normal males, in intact and ovariectomized females alpha 2u-globulin was not detectable in pancreatic hepatocytes. These results indicate that similar to hepatic parenchymal cells pancreatic hepatocytes synthesize alpha 2u-globulin under androgenic regulation. Furthermore, unlike in liver where it is expressed predominantly in perivenular and midlobular hepatocytes, there is no localized difference in the expression of this gene in the transdifferentiated pancreatic hepatocytes.

Alpha-Globulins↗
PubMed1990

Effect of peroxisome proliferators on intrachromosomal and interchromosomal recombination in yeast.

Peroxisome proliferators are a class of non-mutagenic hepatocarcinogens, which induce a similar pleiotropic response such as hepatomegaly, proliferation of the peroxisomes in hepatocytes and hepatocarcinogenesis. Peroxisome proliferators are not detectable by the Ames assay and various other short-term tests. Recently a system for intrachromosomal recombination in yeast (DEL) has been shown to be inducible by a variety of non-mutagenic carcinogens. These include many carcinogens that are not detectable by the Ames assay or by various other short-term tests. In the present study the peroxisome proliferators [4-chloro-6-(2,3-xylidino)-2-pyrimidinyl-thio]acetic acid (Wy-14,643); methyl-2-[4-(p-chlorophenyl)phenoxy]2-methyl propionate (methyl clofenopate); 2-methyl-2[p-(1,2,3,4-tetrahydro-1- naphthyl)phenoxy]-propionic acid (nafenopin); 2-[4-(2,2-dichlorocyclopropyl)phenoxy]2-methyl-propionic acid (ciprofibrate); [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio(N-beta-hydroxyethyl)-acetam ide] (BR-931); and ethyl alpha-p-chlorophenoxyisobutyrate (clofibrate) have been tested for their potential to induce DEL as well as interchromosomal recombination in yeast. No evidence for induction of either system has been found in the presence or the absence of the supernatant (S9) from rat liver homogenate. The data support the notion that peroxisome proliferators are truly non-mutagenic carcinogens.

Anticholesteremic Agents↗
PubMed1990

Differentiation and cell proliferation patterns in rat exocrine pancreas: role of type I and type II injury.

Fully differentiated and functionally specialized acinar cells of the rat pancreas are versatile and adaptable. Acinar cells can be stimulated to divide following administration of a mitogen or after inducing acinar cell necrosis. The degree of compensatory hyperplasia is dependent upon the extent of acinar cell necrosis. Type I injury (subtotal acinar cell necrosis) is followed by marked proliferation of acinar cells leading to complete restitution of the pancreas, whereas subsequent to type II injury (global acinar cell necrosis) there is no restitution of the pancreas because of lack of enough viable cells that have served as precursor cells. Associated with type Ii injury there is proliferation of ductular and periductular cells followed by the development of hepatocytes. In addition, during adverse conditions acinar cells undergo dedifferentiation and form pseudoductular structures. In rats, acinar tissue is a prime target for carcinogens. Transformed acinar cells form foci which are morphologically classified as acidophilic and basophilic lesions. Acidophilic foci which show increased cell proliferation progress to form nodules and acinar cell carcinomas.

Animals↗
PubMed1990

Transdifferentiation of ductular cells into hepatocytes in regenerating hamster pancreas.

The transdifferentiation of regenerating pancreatic cells into hepatocytes in the Syrian golden hamster and Fischer rat is an example of the surprising plasticity of cells in the adult animal. While earlier experiments suggested that these might be derived from acinar cells, unequivocal evidence of this in both models has not been forthcoming. In this paper, we document that pancreatic ductular epithelium in the hamster is the cell of origin and that presumptive hepatocytes can be identified morphologically as early as the 3rd day after the induction of regeneration. The patterns of development of various organelles as characterized by their acquisition of liver-specific protein markers parallels those that have been reported by others during the differentiation of embryonic and postnatal hepatocytes. Colloidal gold-labeled antibody staining of carbamoyl phosphate synthetase, a liver-specific mitochondrial enzyme, and catalase, a peroxisomal enzyme, first appeared 60 hours and 4.5 days postregeneration, respectively. At these times, the morphologic features of the hepatocyte phenotype in the pancreas were ambiguous. Morphometric analysis showed that for both enzymes, the number of gold particles/organelle increased to a maximum by the 9th week. In contrast, urate oxidase, a liver-specific peroxisomal enzyme, was not identified by ultrastructural immunochemistry until the 14th day after regeneration and remained at low levels through the 9th week.

Animals↗
PubMed1989

Evaluation of liver cell proliferation during ciprofibrate-induced hepatocarcinogenesis.

To determine if the carcinogenic potential of peroxisome proliferators is dependent upon their ability to induce cell proliferation, we have investigated the extent of cell proliferation in the livers of rats fed ciprofibrate, a peroxisome proliferator. Male rats were maintained on a diet containing ciprofibrate (0.025% w/w) and killed at selected intervals following 1 week of continuous [3H]thymidine labeling. Evaluation of labeling indices demonstrated a significant increase in cell proliferation during the first week but not in rats killed at the end of 5 and 20 weeks of treatment. Increases in hepatocyte nuclear labeling were found at 40 and 70 weeks of ciprofibrate administration which coincided with the appearance in livers of putative preneoplastic and neoplastic lesions. In a short-term feeding study, ciprofibrate and ethoxyquin were fed to rats at a dietary concentration of 0.025% and 0.5%, respectively, either alone or in combination for 7 days. Ciprofibrate and ethoxyquin either alone or in combination produced marked hepatomegaly and a significant increase in DNA synthesis as demonstrated by [3H]thymidine incorporation and autoradiographic studies. DNA synthesis in the group receiving ciprofibrate and ethoxyquin simultaneously, was slightly more than in animals that received either compound alone, suggesting a synergistic effect, although chronic feeding of these agents together resulted in inhibition of liver carcinogenesis (Rao, M. S. et al. (1984) Cancer Res., 44, 1072-1076). The results of this study further suggest that cell proliferation induced by peroxisome proliferators may be less important in carcinogenesis than peroxisome proliferation induced by these compounds.

Animals↗
PubMed1989

An in vitro demonstration of peroxisome proliferation and increase in peroxisomal beta-oxidation system mRNAs in cultured rat hepatocytes treated with ciprofibrate.

Using the normal adult rat hepatocytes, plated on rat tail collagen-coated dishes and fed a chemically defined medium, we demonstrate here that ciprofibrate at 0.1 mM concentration, increases significantly the mRNA levels of fatty acyl-CoA oxidase, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein, and thiolase (the three enzymes of the beta-oxidation system), and causes peroxisome proliferation. Increase in mRNA levels of these genes was evident within 1 h and was maximal 24 h after the addition of ciprofibrate. In hepatocytes with the basal levels of these enzymes were low and further declined with time. Concomitant treatment of hepatocytes with cycloheximide did not inhibit or superinduce the mRNA levels, indicating that this induction may represent a primary (direct) effect of this compound on the expression of these genes and does not apparently involve short-lived repressor protein(s).

Animals↗
PubMed1989

Formation of 8-hydroxydeoxyguanosine in liver DNA of rats following long-term exposure to a peroxisome proliferator.

The mechanism by which nongenotoxic peroxisome proliferators induce hepatocellular carcinomas in rats and mice remains intriguing. The available experimental evidence suggests that the proliferation of peroxisomes and induction of peroxisome-associated enzymes results in oxidative stress which then leads to tumorigenesis. However, so far no direct evidence for oxidative DNA damage in livers of peroxisome proliferator-treated animals has been established. In the present study we have examined the DNA obtained from the livers of rats treated with ciprofibrate, a potent peroxisome proliferator, for variable periods of time for 8-hydroxydeoxyguanosine (8-OH-dG), an adduct that results from the damage of DNA caused by hydroxyl radical. Administration of ciprofibrate in diet at a concentration of 0.025% for 16, 28, 36, or 40 weeks resulted in progressive increases in the levels of 8-OH-dG. At 16, 28, and 40 weeks of ciprofibrate treatment, the 8-OH-dG in the liver DNA was significantly increased as compared to controls. This increase in 8-OH-dG levels is attributed to persistent peroxisome proliferation resulting from chronic ciprofibrate treatment as no increase in 8-OH-dG was found in liver DNA of rats that received a single large dose of ciprofibrate. The results of this study clearly demonstrate, for the first time, that persistent proliferation of peroxisomes leads to specific oxidative DNA damage.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1989

The nucleotide sequence of a full length cDNA clone encoding rat liver urate oxidase.

Recently we reported the sequence of a cDNA clone (pUOX-1), isolated from a lambda gt11 cDNA library, which encoded for rat liver urate oxidase (EC 1.7.3.3), but this clone lacked the nucleotide sequences encoding the N-terminal region for this enzyme. Using the cDNA insert from the pUOX-1 clone as a probe, we have now isolated a full length cDNA clone, pUOX-2, from a lambda gt10 library by plaque hybridization. Nucleotide sequence analysis of the pUOX-2 clone showed that it has 1379 base pairs with an open reading frame coding for 303 amino acid residues corresponding to a molecular mass of 34,931 daltons. In addition to the open reading frame the pUOX-2 contains 439 bp of 3'-untranslated and 41 bp of 5'-untranslated sequences. The consensus polyadenylation signal AATAAA precedes a stretch of poly(A)+ residues at the 3' end.

Amino Acid Sequence↗
PubMed1989

Oxidative DNA damage caused by persistent peroxisome proliferation: its role in hepatocarcinogenesis.

Peroxisome proliferators are considered as a novel class of hepatocarcinogenic agents because of their non-mutagenic nature and their ability to cause a significant increase in the levels of hydrogen peroxide generating peroxisomal fatty acid beta-oxidation enzyme system in the liver. Sustained increase in the number of peroxisomes in liver has been shown to induce oxidative stress in the liver. Increased levels of H2O2 generation, hydroxyl free-radical formation, lipid peroxidation and accumulation of lipofuscin are found in the livers of rats following long-term treatment with peroxisome proliferators. Recent evidence indicates the presence of 8-hydroxydeoxyguanosine in the liver DNA of rats chronically treated with a peroxisome proliferator suggesting that this may be the basis for carcinogenesis by this class of non-mutagenic carcinogens.

Animals↗
PubMed1989

Differential induction and regulation of peroxisomal enzymes: predictive value of peroxisome proliferation in identifying certain nonmutagenic carcinogens.

Hypolipidemic drugs and certain plasticizers markedly increase the number of peroxisomes in liver parenchymal cells. Continued exposure to peroxisome proliferators has been shown to produce essentially similar pleiotropic responses leading eventually to the development of liver tumors in rats and mice. These agents are not mutagenic in short-term test systems and do not appear to interact with or damage DNA. Accordingly, the events leading to or associated with the induction of peroxisome proliferation have been postulated to play a role in the development of liver tumors. Recent evidence indicates that persistent peroxisome proliferation leads to the formation of 8-hydroxyguanosine in rat liver DNA, which supports the role for oxidative stress. The mRNAs of the three peroxisomal beta-oxidation genes are induced over 20-fold in the livers of rats treated with nafenopin, Wy-14643, BR-931, and other structurally diverse peroxisome proliferators. This increase in beta-oxidation mRNAs is evident within 30 min to 1 hr and was maximal 8 to 16 hr after the administration of a single dose of these agents by gavage. The peroxisomal catalase and urate oxidase mRNAs increase about 2-fold in the livers of rats treated chronically with peroxisome proliferators. These results indicate that peroxisome proliferators differentially regulate different peroxisomal enzymes. The tissue specificity of peroxisomal beta-oxidation gene regulation by xenobiotics supports the contention that the development of liver tumors following exposure to peroxisome proliferators correlates well with the inducibility of peroxisome proliferation and the beta-oxidation genes. Although these agents are known to exert mitogenic response in liver, it is unlikely that stimulation of DNA synthesis alone is responsible for tumor development. Cell proliferation may, however, play a secondary role. The morphological phenomenon of peroxisome proliferation should serve as a simple, sensitive, and valuable biological indicator for the identification of nongenotoxic or nonmutagenic chemicals that may be carcinogenic. An understanding of the cellular and molecular basis of peroxisome proliferation is a prerequisite for the evaluation of toxicological implications of this phenomenon.

Animals↗