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Biomedical subjects

K N Rao

Publications and source records attributed to K N Rao.

At least 19 recordsLinked to original sources
PubMed1995

Inhibition by dehydroepiandrosterone of growth and progression of persistent liver nodules in experimental rat liver carcinogenesis.

Dehydroepiandrosterone (DHEA) inhibits the development of early pre-neoplastic lesions and prevents tumor development in various tissues when given to animals during the initiation/promotion stages of carcinogenesis. Our purpose was to evaluate whether DHEA can also arrest the growth and progression of late lesions, such as persistent nodules (PNs) of rat liver. Male F344 rats were subjected to initiation by diethylnitrosamine followed by selection according to the "resistant hepatocyte" (RH) protocol. Fifteen weeks after initiation, when PNs were present in the liver, the rats were fed a diet with/without 0.6% DHEA for a maximum of 15 weeks. Glucose-6-phosphate dehydrogenase (G6PD) activity was 17- to 20-fold higher in PNs than in normal liver 15-30 weeks after initiation. It significantly decreased, in both liver and PNs, 16 hr after starting DHEA feeding. Further DHEA feeding for 3-15 weeks decreased G6PD activity by 55-58% in both tissues. Eight weeks after starting DHEA, a fall in the proportion of labeled cells, after continuous contact with 3H thymidine for 7 days, was found in nodules. Treatment for 15 weeks with DHEA caused a marked decrease in the number of nodules per liver, as well as in the incidence of PNs with diameters of 3-6 and > 6 mm, respectively, while it did not affect PNs with diameters < 3 mm. Nodules showing patterns of malignant transformation were present in 40% of rats not treated with DHEA, but not in DHEA-treated rats. All of 8 surviving rats not treated with DHEA had carcinomas at the 56th week, while only 1 out of 4 surviving rats treated with DHEA had carcinoma. These data indicate that DHEA inhibits G6PD activity in rat liver and in PNs in vivo. This is associated with growth restraint of PNs and results in inhibition of their progression to malignancy.

Animals↗
PubMed1995

Inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase activity and gene expression by dehydroepiandrosterone in preneoplastic liver nodules.

Previous work has demonstrated that dehydroepiandrosterone (DHEA) strongly inhibits growth and de novo cholesterol (CH) biosynthesis in preneoplastic rat liver. Administration of a mixture of 4 ribo- or deoxyribonucleosides of adenine, guanine, cytosine and uracil/thymine, prevents growth inhibition but not inhibition of CH synthesis. The purpose of this paper was to identify the site of inhibition of CH synthesis by DHEA. Persistent nodules (PNs) were induced, in diethylnitrosamine-initiated male F344 rats, by 'resistant hepatocyte' protocol. Fifteen weeks after initiation, nodule bearing rats and normal controls received a diet containing 0.6% DHEA for 3 weeks. They were then killed. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) activity and mRNA levels were 18- and 14-fold higher, respectively in nodules than in normal liver. DHEA strongly inhibited HMGR activity in both tissues in vivo, but had a slight effect on HMGR activity, when added in vitro to the reaction mixture for determination of this activity. In vivo DHEA treatment caused a 65% decrease in the level of HMGR mRNA in PNs, which, however, does not seem to completely account for the decrease in HMGR activity (83%). Low density lipoprotein receptor (LDL-R) mRNA level underwent a slight decrease in PNs, with respect to control liver, which did not lead to a significant decrease in 125I-LDL binding to LDL-R. DHEA treatment caused 30% and 24% increases in LDL-R expression and 125I-LDL binding, respectively, in nodules. These observations indicate that in addition to HMGR gene expression, increased influx of LDL into preneoplastic cells may contribute to the deregulation of mevalonate synthesis by DHEA. The observation that HMGR activity and gene expression were still 3- to 5-fold higher in PNs of DHEA-treated rats than in control liver, and previous findings of preneoplastic liver cell growth in the presence of relatively low CH synthesis, suggest that even relatively low levels of mevalonate are sufficient for the growth of preneoplastic liver cells.

17-Ketosteroids↗
PubMed1995

Denaturation of pteroylpoly-gamma-glutamyl hydrolase from chicken liver by urea, thiourea and guanidine hydrochloride: altered catalytic properties of the enzyme activated by urea.

The effects of varying concentrations of urea, thiourea and guanidine hydrochloride on the enzyme activity and the isoenzymic polypeptide association of pteroylpoly-gamma-glutamyl hydrolase (EC 3.4.22.12) from chicken liver were studied. Incubation of the enzyme at 4 degrees C with low concentrations of the buffered (100 mM sodium acetate containing 1% ascorbate, pH 4.1) solutions of urea (0.55 M) and guanidine hydrochloride (0.05 M) resulted in stimulation (5- and 2-fold respectively) of the activity of the enzyme whereas at higher concentrations of the denaturants (6 M urea, 1 M thiourea or 2 M guanidine hydrochloride) the enzyme was completely inactivated. However, there was no enzyme activation in response to thiorea treatment. Under specific denaturing conditions the association of two isoenzymic polypeptides was studied. The 0.55 M urea- and 0.05 M guanidine hydrochloride-activated enzyme displayed its disaggregated nonidentical polypeptides I and II (M(r) = 41,000 and 17,300 respectively) on Sephadex G-100 gel filtration, SDS-PAGE and sedimentation analyses. The 8 M urea- and 3 M guanidine hydrochloride-inactivated enzyme on the other hand exhibited a single protein aggregate species of an M(r), 57,000 like the native enzyme. Both unmodified native enzyme and the pCMB-modified PtepolyGlu hydrolase responded similarly to these denaturants. The two constituent active polypeptides polyp-I and polyp-II of the heterodimeric gamma-glutamyl glutamyl hydrolase are dissociated in the presence of 0.55 M urea as evident from the PAGE analyses. Some catalytic properties of the activated enzyme were studied and compared with those of the native enzyme. The urea-activated enzyme displayed a shift in the second pH optimum of the double pH-activity profile (optima at pH 4.1 and pH 5.2) from pH 5.2 to pH 6.0. The activated enzyme has a Km value of 0.59 x 10(-6) M (Vmax, 0.10) for 5-CH3-H4PteGlu4 while the native enzyme has the Km of 0.83 x 10(-6) M (Vmax, 0.03) for this substrate. When the reaction mixtures were incubated with the urea-activated gamma-glutamyl hydrolase, a maximum stimulatory effect on the enzyme activity was observed with the bivalent metal ion Ca2+ whereas the most potent inhibitory effect was observed with the trivalent anion citrate.

Animals↗
PubMed1994

Di(2-ethylhexyl)phthalate-induced changes in liver estrogen metabolism and hyperplasia.

Exposure to a common phthalate, di(2-ethylhexyl)phthalate (DEHP), is associated with liver hyperplasia prior to the development of hepatocellular carcinoma in rodents. The exact mechanism of liver hyperplasia as well as tumorigenesis by this agent is not known. Since other lines of evidence point to estrogens as mediators of liver hyperplastic changes, we investigated whether DEHP exposure might alter hepatic estrogen metabolism and induce hyperplasia. Male Fischer 344 rats were fed either control or 1.2% DEHP-containing diets and sacrificed after 4, 8 and 16 weeks of exposure; activities of several sex hormone-responsive markers were measured. Rats fed DEHP had significantly increased serum estradiol levels, but hepatic activity of both cytosolic and nuclear estrogen receptor (ER) was significantly reduced. The serum content of ceruloplasmin, an estrogen-responsive protein synthesized by the liver, was also reduced, perhaps as a consequence of loss of ER activity. The rise in serum estradiol in DEHP-treated rats may be explained by the observation that these rats showed significant losses in hepatic activity of both a major male estrogen-metabolizing enzyme, estrogen 2-hydroxylase, and a male-specific estrogen-sequestering protein. In contrast to reductions in these activities, the expression of proliferating cell nuclear antigen and mRNAs for both ER and fos increased significantly as a result of exposure to DEHP. Our results suggest that changes in estrogen metabolism, receptor activity and activation of genes for cell proliferation are among the earliest metabolic alterations induced by DEHP. These changes together with the induced hyperplasia could play a crucial role in hepatocellular carcinoma development as a result of continuous exposure to DEHP.

Animals↗
PubMed1994

Physico-chemical properties of thymidylate synthase from Lactobacillus leichmannii: thiol groups, amino acid composition and the terminal end-groups.

Thymidylate synthase (5,10-methylenetetrahydrofolate: deoxyuridylate C-methyltransferase, EC 2.1.1.45) from Lactobacillus leichmannii was completely inactivated after 5 min of heat treatment at 55 degrees C. A remarkable synergistic effect with no loss in activity was noted when 10(-3) M dUMP was added to the enzyme before subjecting to heat treatment. The enzyme got activated in the presence of 2-mercaptoethanol (75 mM) and inhibited by pCMB (I50 = 5 microM). It had 2 free sulfhydryl groups and a single disulfide bond. The two identical subunits of the 74 kDa dimer were possibly bonded by a single disulfide linkage. It had a total of 652 amino acids with methionine as the amino-terminal and alanine as the carboxy-terminal amino acid residues. The carboxy-terminal end-group alanine was preceded by valine, lysine and proline sequentially in that order.

Amino Acids↗
PubMed1994

Pteroyl- and tetrahydropteroylpolyglutamate effects on the catalytic activity of thymidylate synthase from Lactobacillus leichmannii: a novel method for determining gamma-glutamyl chain lengths of the folylpolyglutamates.

Tetrahydropteroylpolyglutamates with longer gamma-glutamyl chain lengths have been found to act as better cofactors than the corresponding monoglutamates for the activity of thymidylate synthase, (5, 10-CH2H4PteGlu: dUMP C-methyltransferase, EC 2.1.1.45) purified from Lactobacillus leichmannii. Contrarily, the pteroylpolyglutamates (unreduced forms) with longer gamma-glutamyl chain lengths act as powerful inhibitors of the same enzyme, the I50 being 2 microM for the tetraglutamate, and inhibition is competitive. The Km and Ki values for the synthetic folylpolyglutamates are identical to those obtained for the natural folylpolyglutamyl forms isolated from Torula yeast (Candida utilis) by the author earlier. A rapid novel method is suggested that could be conveniently used to determine the gamma-glutamyl chain lengths of the folylpolyglutamates employing the direct or indirect linear proportionality relationship observed between the number of gamma-glutamyl residues linked and the Ki and Km values of the enzyme considering the state of oxidation/reduction of the pteridine moiety and the 1-C substituents attached.

Catalysis↗
PubMed1993

Purification, relative molecular mass and subunits of thymidylate synthase from Lactobacillus leichmannii.

Thymidylate synthase (5, 10-methylenetetrahydrofolate: dUMP C-methyltransferase, EC 2.1.1.45) from crude cell extracts of Lactobacillus leichmannii has been purified 190-fold to homogeneity by chromatography on hydroxylapatite, DEAE-cellulose and Sephadex G-100 columns. It has UV absorption maxima at 280 nm. The crude extracts, however, have RNA associated with the native enzyme. This is in line with our earlier observation on the Streptococcus faecium thymidylate synthase [Narasimha Rao K & Kisliuk R L, (1983) Proc Natl Acad Sci USA, 80, 916-920]. Optimal conditions for dTMP synthase activity are: 275 microM (dl)-L-H4PteGlu, 13 mM HCHO, 13 mM MgCl2, 100 microM dUMP and 75 mM 2-mercaptoethanol at pH 7.4 using Tris-HCl buffer. The enzyme has M(r) of 74 kDa, Stokes radius of 1.24 nm and a sedimentation coefficient value of 0.45 S. The enzyme is a dimer composed of 2 identical subunits each with M(r) of 37 kDa.

Lactobacillus↗
PubMed1993

Ternary complex formation with 5-fluoro-2'-deoxyuridylate and the kinetic properties of thymidylate synthase from Lactobacillus leichmannii.

Lactobacillus leichmannii thymidylate synthase (5,10-CH2-H4PteGlu:dUMP C-methyltransferase, EC 2.1.1.45) forms a tight and stable covalently bonded ternary complex with the inhibitor 5-FdUMP in the presence of the cofactor 5,10-CH2-H4-PteGlu. 'Filter assay' employing the radioactive nucleotide ligand showed that 2 moles of FdUMP are bound per mole enzyme during the ternary complex formation with the L. leichmannii dTMP synthase. This is in line with our earlier observation on the Streptococcus faecium thymidylate synthase [Narasimha Rao, K & Kisliuk R L (1983), Proc Natl Acad Sci USA, 80, 916-920]. The enzyme has Km values of 6.3 x 10(-6) M, 8.2 x 10(-5) M and 1.0 x 10(-4) M for dUMP, (dl)-L-H4PteGlu and Mg2+ respectively; Vmax for dUMP, (dl)-L-H4PteGlu and Mg2+ are; 0.55, 0.5 and 1.1 respectively. It has K(i) values of 6.7 x 10(-6) M, 2.2 x 10(-6) M, 5.0 x 10(-5) M and 2.0 x 10(-4) M for FdUMP, dTMP, MTX and Ca2+ respectively. The type of enzyme inhibition with FdUMP, dTMP, MTX and Ca2+ was competitive. dTMP Studies clearly show the 'end product' inhibition of the enzyme.

Binding Sites↗
PubMed1992

Synthesis and pharmacological evaluation of some N-[pyridyl(phenyl)carbonylamino]methyl-1,2,3,6-tetrahydropyrid ines.

Reaction of some picolines 5 with 1-chloro-2,4-dinitrobenzene (6) in acetone furnished methyl-substituted 2,4-dinitrophenylpyridinium chlorides 7. Further reaction with phenyl(pyridyl)carbonyl hydrazides 8 at room temperature furnished isolable 2,4-dinitroanilino derivatives 9, which were then refluxed in a water:dioxane mixture (1:4, v/v) to furnish the methyl-substituted phenyl(pyridyl)carbonyl iminopyridinium ylides 10. Reduction of the ylides with NaBH4 finally gave rise to the desired methyl-substituted phenyl(pyridyl)carbonylamino-1,2,3,6-tetrahydropyridines 11. The anti-inflammatory activities of 11a-11l were determined with the carrageenan-soaked sponge model of inflammation in Sprague-Dawley rats, and the analgesic effects of these derivatives were assessed by suppression of acetic acid-induced writhing in male Swiss albino mice. All compounds tested showed moderate to good anti-inflammatory and analgesic effects compared with indomethacin. Compound 11k was the most active analgesic, and 11h was the most effective anti-inflammatory agent among the methyl-substituted tetrahydropyridines.

Animals↗
PubMed1992

Nutritional status of children of urban leprosy patients staying at preventoria based on biochemical parameters.

Measurements of nutritionally relevant biochemical and endocrine variables were made on 60 apparently healthy children (group A) whose parents suffered from leprosy and who had been separated at the age of 4 years and brought up in preventoria. Most of the measurements were also made on a comparison group of healthy children from the same poor socio-economic class (group B). In both groups the serum concentrations of cholesterol and triglycerides were well below those found in Western populations. Almost all the children in both groups were anaemic, but serum iron and ferritin levels were satisfactory. Folate and vitamin B12 levels were measured in group A only and were low in a significant proportion. Deficiency of these water-soluble vitamins may be a cause of the anaemia. Low albumin levels were found in 40% of group A children, compared with 2% in group B. The concentrations of calcium and magnesium were lower and that of phosphate higher in group A than in B. In both groups one-third of the children had low levels of serum zinc. Fifteen per cent of group A children had biochemical evidence of vitamin A deficiency, but none were deficient in vitamin E. Levels of total T3 and total T4 were below the lower limit of normal in a substantial proportion of children in both groups. Concentrations of parathyroid hormone were increased in parallel with the low values for serum calcium. Radiological studies of ossification centres in 57 group A children showed delayed maturation in 11 cases. The relevance of these findings to previous studies of the children of lepers in India is discussed.

Adolescent↗
PubMed1991

Resistance of female Fischer-344 rats to the hepatonecrogenic and hepatocarcinogenic actions of a choline-devoid diet.

A series of experiments was performed to investigate the response of female Fischer-344 rats to a choline-devoid (CD) diet. In contrast to findings previously made in male Fischer-344 rats, hepatocellular carcinomas did not develop in females chronically fed the diet. Their liver actually showed only minimal histopathological changes. For these reasons, the steatogenic and hepatonecrogenic actions of a CD diet were compared in male and female Fischer-344 rats. Young adult females were found to be largely resistant to both. The results were taken as further evidence of the primary and essential role played by an enhanced cell turnover in the pathogenesis of the carcinomas induced in male Fischer-344 rats by this non-chemical, nutritional model of hepatocarcinogenesis. A high incidence of preneoplastic and benign lesions developed in breast, pancreas or stomach of females chronically fed the CD diet. However, a similar spectrum and high incidence of lesions was observed in control rats fed a choline-supplemented diet. These findings were attributed to an enhanced occurrence of spontaneous lesions, most likely due to the high fat content (15%) of the two diets used.

Animals↗
PubMed1991

Differential effects of dehydroepiandrosterone and deoxyribonucleosides on DNA synthesis and de novo cholesterogenesis in hepatocarcinogenesis in rats.

Previous studies from our laboratory have shown that dehydroepiandrosterone (DHEA), an inhibitor of glucose-6-phosphate dehydrogenase (G6PD), prevents the development of gamma-glutamyltranspeptidase (GGT)-positive foci in the early stages of hepatocarcinogenesis in rats. Since high rates of DNA and cholesterol (CH) synthesis are observed during promotion of carcinogenesis, and mevalonate (MVA), or some other intermediates of CH synthesis, could be mediators of DNA synthesis, we investigated the effect of DHEA on CH synthesis in rat liver during the development of GGT-positive foci. Hepatocarcinogenesis was induced by diethylnitrosamine in female Wistar rats by the Solt-Farber protocol (initiation/selection) with and without phenobarbital treatment. A 15 day treatment with DHEA (0.6% in the diet), started after selection, caused a great fall in labeling and mitotic indices of GGT-positive foci, which was prevented by the simultaneous administration of a mixture of four deoxyribonucleosides (DRNs) of adenine, guanine, cytosine and thymine or four ribonucleosides (RNs) of adenine, guanine, cytosine and uridine, but not by the corresponding bases. DHEA greatly inhibited G6PD activity and the production of ribulose-5-phosphate, without affecting NADPH levels, due to the compensatory increase in malic enzyme and isocitric dehydrogenase activities. Serum lecithin/cholesterol acyltransferase activity underwent a reduction in conditions allowing a rapid growth of GGT-positive tissue (absence of DHEA or presence of DHEA plus DRNs or RNs). Liver slices isolated from DHEA-treated rats showed a rise in CH content, coupled with a 80% fall in the incorporation of labeled acetate, but not of labeled MVA, into CH. A 25 day treatment of rats subjected to initiation/selection, started after the appearance of persistent nodules, caused a 36 and 78% fall in the incorporation, in vivo, of 3H2O into nodular and surrounding liver CH respectively. DRN did not counteract DHEA-induced inhibition on CH synthesis. Thus DHEA inhibits the CH biosynthetic pathway before MVA synthesis, in conditions (presence of DHEA plus DRN/RN) allowing rapid growth of preneoplastic lesions. Therefore, the development of these lesions does not need the synthesis of large amounts of CH and CH metabolites. Thus, the antipromotion effect of DHEA may depend on a decreased availability of pentose phosphates for DNA synthesis.

Animals↗
PubMed1991

Synthesis and anti-inflammatory activities of some N-[pyridyl(phenyl)carbonylamino]-tert-butyl/phenyl-1,2,3,6- tetrahydropyridines.

Nucleophilic attack of tert-butyl/phenylpyridines 3 on 1-chloro-2,4-dinitrobenzene 4 results in the formation of tert-butyl/phenyl substituted 2,4-dinitrophenylpyridinium chlorides 5. Benzoyl hydrazide and pyridyl acid hydrazides 6 were reacted with the pyridinium chlorides 5 furnishing the 2,4-dinitroanilino derivatives 7, which were subsequently hydrolyzed with water: p-dioxane to yield N-[pyridyl(phenyl)carbonylimino]-tert-butyl/phenylpyridinium ylides 8. The title compounds 9, N-[pyridyl(phenyl)carbonylamino]-tert-butyl/phenyl-1,2,3,6- tetrahydropyridines, were obtained by sodium borohydride reduction of the pyridinium ylides 8. The anti-inflammatory activities of compounds 9a-p were determined using the carrageenan-soaked sponge model of inflammation in Sprague Dawley rats. All compounds tested showed moderate to good anti-inflammatory effects compared to indomethacin. Compounds 9b, 9c and 9p were the most active analogs of the group in this model.

Animals↗
PubMed1990

A survey of plant crude drugs of Rayalaseema, Andhra Pradesh, India.

An ethnobotanical survey of Rayalaseema of Andhra Pradesh was carried out during 1985-1988. One hundred and thirty-one useful plants currently used by the tribal and non-tribal inhabitants for treating different ailments are presented. Most of the uses of the plants reported by herbalists appear not to have been recorded hitherto. The study reveals some interesting information about the mode of plant use in various ailments either singly or in combination. It has been observed that though the tribes studied live under the same environment and use the same plant species for treating diseases, their prescriptions are quite different. This indicates that these tribes still retain their own traditions so far as treatments are concerned.

Botany↗
PubMed1990

Genetics and diet: synergism in hepatocarcinogenesis in rats.

In previous studies we have shown that male rats carrying genes controlling growth and reproduction (grc) linked to the major histocompatibility complex (MHC) to be more susceptible to N-2-acetylaminofluorene than rats without grc genes. In the present studies we show that by manipulation of the diet of grc rats, hepatocarcinogenesis induced by another carcinogen can be altered. Male rats with the grc gene (R16) and wild type (ACP) were initiated with diethylnitrosamine (DEN) (200 mg/kg body weight). Some were fed laboratory chow (LC) for 9 months; others were fed a choline-supplemented (CS) or a choline-deficient (CD) diet. The rats were killed at various time periods and the liver sections were stained with H&E and for gamma-glutamyltranspeptidase (GGT). After 9 months on LC, the livers of R16 showed greater size and number of GGT-positive foci, bile duct proliferation, cellular atypia, cirrhosis, and nodular hyperplasia than the ACP. While the first hepatocellular carcinoma in R16 fed either a CS or LC was seen at 9-10 months, one R16 rat fed a CD diet had liver cancer at 4 months. On a CS diet the R16 showed greater GGT-positive foci at 2 months than the ACP. On a CD diet the R16 showed even greater size and number of GGT-positive foci. At 12 months, 15 of 22 (68%) of the R16 rats on a CD diet had liver cancer and seven of 24 (29%) of the R16 on a CS diet. Of the ACP, none of 15 (0%) on CS and one of 18 (6%) on CD diet had liver tumors. The results show that the grc genes confer high susceptibility to liver cancer, which is enhanced by a CD diet, suggesting synergism between genetics and diet.

2-Acetylaminofluorene↗
PubMed1990

A study on nutrition, growth and development of a high-risk group of children of urban leprosy patients.

This paper describes a cross-sectional study of the physical development of a high-risk group of 182 socially deprived healthy children of leprosy patients ranging from preschool age to early teens. They were rescued at the age of 4 years from the distress of leprosy colonies where they were born, and brought up in Government Homes (Preventorium) under better environmental conditions. Of them 135 children could be followed clinically for 10 years for the development of childhood leprosy. Another 94 children of leprosy patients living with their parents were included for comparison. A group of 158 normal children of similar economic status and age group were included as controls. It was observed that, although better environment, food and training were provided in the Preventorium, so that the children could be brought into the national mainstream, nevertheless 5 children developed an indeterminate type of leprosy during the course of 10 years. This is the first report of growth and development of children of leprosy patients from the Indian sub-continent.

Adolescent↗