Effect of chlorinated naphthalenes and terphenyls on the activities of drug metabolizing enzymes in rat liver

γ-Aminobutyric acid-α-ketoglutarate transaminase from pig brain is irreversibly inactivated by 4-amino-5-halopentanoic acids. Protection from inactivation by the natural substrates, the pH dependence of inactivation and the incorporation of 1.7 moles of radioactive inhibitor per mole of enzyme from (S)-[U-¹⁴C]-4-amino-5-chloropentanoic acid suggest a covalent adduct at the active site of the enzyme. A mechanism-based inactivation is proposed.     

Effect of masheri, a pyrolysed tobacco product on carcinogen metabolizing enzymes

Studies on the modulation of the carcinogen metabolizing enzymes on treatment with masheri extract (ME) and benzo (a) pyrene (B (a)P), were carried out in male Sprague Dawley rats (12 weeks old) fed a nutritionally adequate standard diet. Injection (ip) of ME and B (a) P at 3/4 LD50 dose given in 3 doses at 24 hr interval increased the phase I activating enzymes, viz. cytochrome P-450, benzo (a) pyrene hydroxylase and benzphetamine demethylase while both ME and B (a) P significantly depleted glutathione content and decreased glutathione-S transferase activity. Furthermore, the same treatment of ME and B (a) P significantly depleted the hepatic vitamin A pool while a concommittant increase in vitamin C content was observed.     

Effect of iodide-deficiency on rat mammary gland.

When rats are kept iodide-deficient, atrophy and necrosis takes place in the mammary gland and areas of dysplasia and atypia are seen. Administration of estradiol to iodide-deficient rats stimulates cell division in the gland and leads to the formation of alveoli. Continued stimulation by estradiol produces changes in the newly-formed alveolar cells. Their nucleoli are altered and show a separation of components. Ribosomes and lipid droplets increase and the cells synthesize large vacuoles containing protein. The secretion of great quantities of this material into areas of the tissue where regressive changes have occurred undoubtedly contributes to the formation of cysts within the gland. The present findings indicate that iodide-deficiency alters the structure and function of mammary gland alveolar cells and makes them highly sensitive to stimulation by estradiol.     

Effect of thyroid hormones on the activities of hepatic alcohol metabolizing enzymes.

Treatment with thyroxine or triiodothyronine for 7 days in order to simulate a hyperthyroid state results in an enhanced activity of the microsomal ethanol oxidizing system. Conversely, a decrease of hepatic alcohol dehydrogenase activity was observed under these experimental conditions, whereas hepatic catalase activity remained unchanged. These findings suggest that if chronic ethanol consumption simulates a “hyperthyroid hepatic state”, increased rates of ethanol metabolism observed following prolonged alcohol intake might therefore be attributed at least in part to an induction of microsomal ethanol oxidizing system activity in the liver.     

Role of vitamin A in chemical carcinogenesis in the mammary gland]

The effect of feeding rats with high doses of vitamin A on the distribution of polycyclic hydrocarbon, 7,12-dimethylbenzanthracene (DMBA) and its metabolites in different organs and blood, and also on the metabolic rate in the liver was studied following intravenous injection of the carcinogen. Hypervitaminosis A resulted in a significant decrease of the level of DMBA and its metabolites in all the organs investigated and in the blood. The rate of DMBA metabolism in the liver of the animals rose with the increase of the vitamin A dose.     

Biosynthesis of myo-inositol in rat mammary gland. Isolation and properties of the enzymes

myo-Inositol 1-phosphate synthase (EC 5.5.1.4) and 1l-myo-inositol 1-phosphatase (EC 3.1.3.25) were isolated and partially purified from lactating rat mammary gland. The synthase had an apparent molecular weight of 290,000 as determined by gel filtration; its pH optimum was 7.2, and the K_m for glucose 6-phosphate was 0.5 mm. No other compound could act as a substrate, but the synthase was inhibited 100% by d-gluconic acid 6-phosphate, 54% by d-fructose 6-phosphate, 31.8% by d-galactose 6-phosphate, and 29.6% by d-mannose 6-phosphate each at 5mm. Activity was stimulated 2-fold by the addition of 1 mm NAD⁺ and 40% by 14 mm ammonium ions, whereas it was inhibited by 30% in the presence of 1 mm NADH and by 93.6% when incubated with 1 mmp-mercuribenzoate. Reagents which interfere with Schiff-base formation, pyridoxal 5′-phosphate and trinitrobenzenesulfonate, inhibited the enzyme, but EDTA was without effect.The 1l-myo-inositol 1-phosphatase from rat mammary tissue appears to exist in a native tetrameric form of 210,000 as determined by gel filtration which, upon heating at 70 °C for 15 min, is converted into a stable monomer of approximately 52,000. Mg²⁺ (1.5 mm) was an absolute requirement for activity though Mn²⁺ gave 17% of the activity provided by Mg²⁺. Sodium, potassium, or ammonium ions were stimulatory, but lithium ions were strongly inhibitory. 1l-myo-Inositol 1-phosphatase specifically cleaved 1l-myo-inositol 1-phosphate and was 60% as active toward l-α-glycerol phosphate with only minor activity toward other phosphorylated compounds. The pH optimum was 8.0 and the K_m for 1l-myo-inositol 1-phosphate was 0.8 mm.     

Amino acid metabolizing enzymes in rat submaxillary gland, normal or neoplastic, and in pancreas.

The activities of 12 enzymes, many related to ornithine metabolism, were measured in rat submaxillary gland, submaxillary gland tumors and pancreas. In submaxillary gland, the activities of arginase, ornithine aminotransferase, pyrroline-5-carboxylate reductase and glutamine synthetase were high, but no ornithine transcarbamylase or proline oxidase could be detected. In the fetal submaxillary gland, arginase was at almost adult levels while ornithine aminotransferase reached 50% of its adult value postnatally. Submaxillary tumors deviated from their cognate tissue by lower levels of amino acid metabolizing enzymes and by high concentrations of thymidine kinase. In pancreas, none of the pyrroline-5-carboxylate metabolizing enzymes were as high as in either liver or submaxillary gland. The outstanding activities were those of gamma-glutamyl transpeptidase and glutamate dehydrogenase. Although arginase activities in submaxillary gland and pancreas were quantitatively similar, they differed qualitatively: submaxillary gland contained the same variant as liver while the pancreatic isozymes resembled those of other nonhepatic tissues.     

Relationship between RNA polymerase and protein kinase activities in rat mammary gland nuclei.

1. Extracts from rat mammary gland nuclei contain cyclic AMP -independent protein kinases which phosphorylate casein rather than histone. 2. A major increase in nuclear protein kinase activity occurred during late pregnancy and was maintained with the onset of lactation. 3. Two major peaks of activity were resolved by chomatography of nuclear extracts on DEAE-Sephadex; the first (NI) appeared in the void volume and the second (NII) was eluted by 0.05-0.12 M ammonium sulfate. Several other regions of lesser activity were also present. 4. Protein kinases in the cytosol 105,000 times g supernatant, precipitated by 70 percent ammonium sulfate, dialyzed against buffer, and chromatographed on DEAE-Sephadex, yielded a major components phosphorylated histone in preference to casein, and this was stimulated by cyclic AMP if histone was the substrate, but only the first (void volume) fraction was cyclic AMP-dependent when casein was used. 5. Most of RNA polymerases Ib and II, derived from the nucleolus and nucleoplasm, respectively, appeared in column fractions distinct from those containing the major NI and NII protein kinases. 6. Cyclic AMP altered the amount of RNA product synthesized by polymerases Ib and II, but the explanation for this is unknown. Due to their elution profiles and cyclic AMP-independence, protein kinases NI and NII are excluded from playing a catalytic role in these effects; participation of quantitatively minor protein kinases which co-elute with polymerase Ib and II is not yet excluded.     

Changes in the activities of enzymes of the biosynthetic pathway of the nicotinamide nucleotides in rat mammary gland during the lactation cycle

1. The activities of NMN pyrophosphorylase, NMN adenylyltransferase and NAD kinase in the mammary glands of rats at different stages of pregnancy, lactation and involution were measured. 2. NMN pyrophosphorylase has a low activity early in pregnancy, but its activity increases at parturition and in early lactation to reach a maximum at the tenth day of lactation, after which it remains constant until it declines abruptly in involution. 3. NMN adenylyltransferase is already quite active by the tenth day of pregnancy and its activity does not rise further in the second half of gestation. After a sharp rise in activity at parturition, the activity of the enzyme declines slowly throughout the period of lactation and, more sharply, in involution. 4. NAD kinase has a low activity for most of pregnancy, but its activity rises at parturition to a value at 2 days of lactation that is maintained until the tenth day. Between the tenth and fifteenth days of lactation the activity almost doubles, but falls sharply in mammary involution. 5. The relation of the activities of these enzymes to the rates of synthesis of NAD and NADP is discussed.     

Rhythmic growth and carbon allocation in Quercus robur. Sucrose metabolizing enzymes in leaves

The high sucrose phosphate synthase (SPS) capacity and the low soluble acid invertase activity of mature leaves of the first flush of leaves remained stable during second flush development. Conversely, fluctuations of sucrose synthase (SS) activity were in parallel with the sucrose requirement of the second flush. Sucrose synthase activity (synthesis direction) in first flush leaves could increase in 'response' to sink demand constituted by the second flush growth. Only the ptotosynthates provided by flush mature leaves were translocated for a current flush, while the starch content of these leaves remained stable. After their emergence, second flush leaves showed an increase in SPS and SS (Synthetic direction) activities. The high sucrose synthesis in second flush leaves was used for leaf expansion. When young leaves were 30% fully expanded (stage II20), SPS activity showed little change whereas SS activity declined rapidly toward and after full leaf expansion. The starch accumulation in the young leaves occured simultaneously with their expansion. Developing leaves showed a high level of acid invertase activity until maximum leaf expansion (stage II1). In first and second flush leaves, changes in acid invertase activity correlated positively with changes in reducing sugar concentrations. Alkaline invertase and sucrose synthase (cleavage direction) activities showed similar changes with low values when compared with those of acid invertase activity, especially in second flush leaves. The present results suggest that soluble acid invertase was the primary enzyme responsible for sucrose catabolism in the expanding common oak leaf.     

Chemoprotective influence of Zanthoxylum sps. on hepatic carcinogen metabolizing and antioxidant enzymes and skin papillomagenesis in murine model

In the present study, the putative potential of pericarp of dried fruit of Zanthoxylum (Rutaceae Family), a common spice additive in India's west coast cuisines, in protecting against carcinogenesis has been reported. Extract from dried fruit of Zanthoxylum was orally administered to mice at two dose levels: 100 and 200 mg/kg body wt. for 14 days. Results reveal bifunctional nature of Zanthoxylum species as deduced from its potential to induce phase-I and phase-II enzyme activities associated with carcinogen activation and detoxification in the liver of mice. Hepatic glutathione S-transferase and DT-diaphorase were found significantly elevated by the treatment. Zanthoxylum was also effective in augmenting the antioxidant enzyme activities of glutathione peroxidase, superoxide dismutase and catalase albeit significantly by high dose of the extract (P < 0.05; P < 0.01). Reduced glutathione was also significantly elevated in the liver of treated animals (P < 0.05). The present study also investigated peri-initiation application of acetone extract of Zanthoxylum on initiated mouse skin. Results showed a significant reduction in tumor incidence from 68% to 36% (P < 0.05); as well as, a reduction in tumor burden per effective mouse from 3.87 to 0.72 (P < 0.01). Cumulatively, the findings strongly suggest cancer chemopreventive potential of Zanthoxylum sps.