Alterations in the activities of intestinal enzymes in vitamin-C-deficient guinea pigs

The effect of vitamin C deficiency on various enzymes of the intestinal epithelium has been studied in guinea pigs. Brush border sucrase and alkaline phosphatase activities were considerably enhanced (p less than 0.001), but leucine aminopeptidase levels were reduced in scorbutic animals compared to the control group. There was essentially no change in the activity of maltase under these conditions. Kinetic studies with sucrase and alkaline phosphatase in control and scorbutic animals revealed that augmentation of the enzyme activities in scurvy is due to enhanced enzyme contents. Lactate dehydrogenase, succinate dehydrogenase, glucose-6-phosphatase and Mg+2 ATPase also exhibited reduced activities in the intestine of vitamin-C-deficient animals. Observed alterations in the activities of intestinal enzymes in scurvy were restored to control levels upon feeding of vitamin C to scorbutic guinea pigs.     

Induction of osteoblastic cell differentiation by forskolin. Stimulation of cyclic AMP production and alkaline phosphatase activity

The effects of forskolin on differentiation of osteoblastic cells (clone MC3T3-E1) cultured in alpha-minimum essential medium containing 0.1% bovine serum albumin were investigated by assays of intracellular cyclic AMP level and alkaline phosphatase activity in the cells. Forskolin increased cyclic AMP production in the cells in a dose-related manner, the maximum increase being 250-fold above that of the controls. Alkaline phosphatase activity in the cells was also elevated as early as 24 h and rose to nearly its maximum at 48 h. The elevation was dose-dependent, with a maximum increase at 5 X 10(-6) M forskolin. Forskolin and prostaglandin E2 showed a supraadditive effect on cyclic AMP production in the cells and had an additive effect on alkaline phosphatase activity, whereas forskolin and dibutyryl cyclic AMP had little additive effect on either cyclic AMP production or enzyme activity. These results suggest that cyclic AMP is closely linked to the differentiation of osteoblastic cells in vivo.     

myo-inositol action on gerbil intestine: alterations in alkaline phosphatase activity upon phosphatidylinositol depletion and repletion in vivo

The influence of phosphatidylinositol (PI) on intestinal alkaline phosphatase activity was studied in myo-inositol deficient gerbils. A reduction of membrane PI in intestinal mucosa to 30-40% of the control was produced by feeding female gerbils a myo-inositol-deficient diet containing coconut oil for 2 weeks. As expected, the animals developed typical intestinal lipodystrophy with abnormal fat accumulation. In the PI-depleted animal, intestinal alkaline phosphatase activity was reduced to 20-30% of the control group. The levels of both membranous and soluble enzymes in intestinal mucosa were affected, but there were no changes in liver, kidney and plasma levels. When the lipodystrophic gerbils were given dietary myo-inositol, the complete repletion of intestinal membrane PI to the control level occurred 36 h later, whereas membrane-bound alkaline phosphatase activity in intestine was not restored to the control level until 72 h later. Administration of cycloheximide or actinomycin D did not block this enzyme induction. Lymphatic output of triacylglycerol into the bloodstream was stimulated 10-fold at 18 h of myo-inositol repletion, but there was no parallel increase in the activity of alkaline phosphatase in plasma during this early phase of intestinal recovery. Thus, these data suggest a possible regulatory role of PI in the processing and/or turnover of alkaline phosphatase in vivo, but a negative role of alkaline phosphatase in lipid transport across gerbil intestine.     

Organ-selective induction of cytochrome P-450-dependent activities by indole-3-carbinol-derived products: influence on covalent binding of benzo[a]pyrene to hepatic and pulmonary DNA in the rat.

Indole-3-carbinol (I3C) is a dietary modulator of carcinogenesis that can reduce the level of carcinogen binding to DNA. I3C-derived products are potent inducers of certain cytochrome P-450(CYP)-dependent enzyme activities. To investigate whether the protective effects of I3C against carcinogen damage to DNA are associated with increased activities of CYP1A1 enzymes, we examined the relationship of I3C-mediated organ-specific CYP enzyme induction with total levels of benzo[a]pyrene (BP) binding to hepatic and pulmonary DNA of rats. Oral intubation (PO) of I3C (500 mumol/kg body wt.) in 10% DMSO in corn oil produced after 20 h, increases in ethoxyresorufin O-deethylase (EROD) activities (associated with CYP1A1 isozyme) of 700-fold, 245-fold and 36-fold in small intestine, lungs and liver, respectively, compared with activities in untreated controls. Hepatic aryl hydrocarbon hydroxylase (AHH) activity was increased 4-fold under these conditions. Pentoxyresorufin O-depentylase (PROD) activity (associated with CYP2B isoenzyme) was increased 6-fold in the liver but was unaffected in lung and small intestine. Intraperitoneal injection (IP) of I3C (500 mumol/kg body wt.) produced no significant change in EROD or PROD activities in lung, liver, or small intestine. PO administration of the acid reaction mixture (RXM) of I3C increased hepatic AHH activity (5-fold) and EROD activities in small intestine (650-fold), lung (100-fold) and liver (18-fold). IP administration of RXM (equivalent to 500 mumol I3C/kg body wt.) significantly increased only EROD activity in lung and liver, but did not affect EROD activity in small intestine, AHH activity in liver, or PROD activity in any of the organs examined. Twenty hours after inducer treatment, half of the rats were treated PO with 0.2 mumol [3H]BP in corn oil. Analysis of tissues 5 h after BP administration indicated that compared with untreated controls, administration of I3C and RXM by either route reduced by 30-50% the level of BP binding to hepatic DNA, an effect that was not correlated to CYP1A1 enzyme induction in any of the organs examined. However, PO administration of I3C and RXM produced a 50-70% decrease in carcinogen binding to pulmonary DNA, while IP administration of inducers had no effect on DNA binding in this organ. These results with the lung are consistent with an increased presystemic clearance of BP in the intestine and are discussed in terms of the role of induction of intestinal CYP1A1 activity in the decreased lymphatic and venous transport of unmetabolized BP to the lung.     

Cholinergic-stimulated alkaline phosphatase secretion and phospholipid synthesis in guinea pig seminal vesicles

Incubation of slices of seminal vesicles of the guinea pig with cholinergic drugs led to an enhanced secretion of alkaline phosphatase. Incubation with carbamylcholine also stimulated the incorporation of P³² into the phospholipid fraction. Both cholinergic effects required a supply of energy since dinitrophenol was inhibitory. The stimulation of enzyme secretion and phospholipid synthesis by carbamylcholine was completely abolished by atropine. Omission of calcium ions from the incubation medium and pre-treatment of the slices with ethylenediaminetetraacetic acid (EDTA) caused a marked reduction in alkaline phosphatase secretion induced by carbamylcholine but had no effect on incorporation of P³² into phospholipids. Adenergic agents such as epinephrine, norepinephrine and isoproterenol did not influence these two processes. Addition of cyclic AMP, dibutyryl cyclic AMP and a phosphodiesterase inhibitor was also ineffective. The incorporation of P³² into the various phospholipids of the seminal vesicle was examined. In the presence of carbamylcholine, there was a marked increase in the P³²-specific activities of phosphatidylinositol (nearly 6-fold) and of phosphatidylserine (about 1.5-fold). These observations indicate that the guinea pig seminal vesicle, a large hollow organ composed of a single layer of epithelium, is ideally suited for studies concerning the biochemistry of macromolecular secretion.     

A possible mechanism of induction and translocation into blood stream of rat alkaline phosphatase activity by bile duct ligation

We investigated the effects of bile duct ligation on alkaline phosphatase (ALP) activities in liver, calvarium, duodenum, and ileum in rats and its possible mechanism of action. ALP isozyme activities in the ligated rats were significantly elevated in the liver and duodenum, while those in the ileum and calvarium were markedly decreased. The ALP isozyme activity elevated by the ligation was obviously suppressed by prior administration of indomethacin, an inhibitor of prostaglandin synthesis. Moreover, phorbol ester also elevated the ALP activity as well as the phosphatase level in the ligated rat. However, other drugs, such as an inhibitor of protein kinase C and calmodulin, showed different effects: calmodulin stimulated an 11.0-, 1.3-, or 1.5-fold increase in ALP activity in the ileum, duodenum, or calvarium, respectively; whereas the hepatic enzyme activity was not affected. The induction by calmodulin was markedly different from that by the ligation. Moreover, imipramine, an inhibitor of protein kinase C, had little effect. These results suggest that prostaglandin is a possible ALP inducer in ligated rats, probably working by elevating the cAMP level. On the other hand, the ligation induced simultaneously de novo synthesis of the membranous and soluble ALP isozymes; and the release rate of the soluble enzyme was greater than that of the membranous isozymes, indicating that the soluble enzyme might be a main source of the induced serum ALP. Lectin affinity chromatography indicated that the soluble enzyme or induced serum enzyme may contain more fucose than that of the membranous one, suggesting that the sugar moiety in the ALP molecule may relate to the clearance of ALP from or its release into the circulation.     

Characterization of brush border membrane-bound alkaline phosphatase activity in different segments of the porcine small intestine

This study was conducted to characterize enterocyte apical membrane-bound alkaline phosphatase activity in different segments of the porcine small intestine. Duodenal, jejunal, and distal ileal segments were isolated from three 26-kg pigs and enterocyte brush border membrane, enriched between 19- and 24-fold in sucrase specific activity, was prepared by Mg(2+) precipitation and differential centrifugation. With P-nitrophenyl phosphate as substrate, the optimum pH for porcine brush border membrane-bound alkaline phosphatase activity was defined to be 10.5 for all three segments. At the optimal pH, the kinetics of membrane-bound alkaline phosphatase were determined for the three intestinal segments. The affinity of this enzyme (K(m), mM) in the jejunum (0.64 +/- 0.07) was four times greater than that in the duodenum (2.75 +/- 0.59) and the distal ileum (2.71 +/- 1.14). These results indicate that different isomers of membrane-bound alkaline phosphatase might have been expressed in different segments of porcine small intestine. The maximal specific activity (V(max), micromol/mg protein . min) of this enzyme was highest in the duodenal (7.74 +/- 0.95), intermediate in the jejunal (4.31 +/- 0.18), and lowest in the distal ileal (3.53 +/- 0.84) brush border membrane. Therefore, the maximal specific activity of brush border membrane-bound alkaline phosphatase along the intestinal longitudinal axis in growing pigs decreases from the duodenum toward the distal ileum.     

The effects of prostacyclin analogue ZK 36374 and thromboxane synthetase inhibitor UK 38485 on mesenteric ischemia in guinea pigs.

The effects of ZK 36374, a prostacyclin analogue and UK 38485, a thromboxane synthetase inhibitor were studied in guinea pigs after performing mesenteric arterial occlusion. In this study, while ZK 36374 significantly lowered the alkaline phosphatase and creatine phosphokinase values two hours after mesenteric arterial occlusion when compared with the control group (p less than 0.005), UK 38485 did not induce any change. In guinea pigs, when given together, ZK 36374 and UK 38485 lowered the enzyme levels to preligation values and the difference was nonsignificant (p greater than 0.1). The histopathologic investigation of the small intestine after giving ZK 36374 and UK 38345 together revealed minimal changes. These findings stress the importance of preserving the PGI2 levels in the PGI2/TXA2 ratio in preventing the increase of lysosomal enzyme levels and histopathologic changes after mesenteric arterial occlusion in guinea pigs.     

Increase in hepatic tyrosine aminotransferase mRNA during enzyme induction by N6,O2'-dibutyryl cyclic AMP.

Tyrosine aminotransferase mRNA was quantitated by translation in a cell-free system derived from wheat germ followed by specific immunoprecipitation of the newly synthesized enzyme subunit. Hepatic poly(A)-containg RNA prepared from rats treated for 4 h with N6, O2'-dibutyryl cyclic AMP and theophylline was approximately 5.6 times more active in directing the synthesis of the tyrosine aminotransferase subunit relative to untreated controls. The overall template activity of the RNA prepared from control and cyclic AMP-treated animals was virtually identical, demonstrating that the cyclic nucleotide effect was specific for the tyrosine aminotransferase mRNA. At all times, after a single injection of dibutyryl cyclic AMP and theophylline, the increase in hepatic enzyme activity was accompanied by corresponding induction in the level of functional tyrosine aminotransferase mRNA. Other inducers of tyrosine aminotransferase, such as glucagon and hydrocortisone, also increased the level of tyrosine aminotransferase mRNA in proportion to their effect on enzyme activity. The RNA polymerase II inhibitor, alpha-amanitin, completely blocked the dibutyryl cyclic AMP-mediated increase in tyrosine aminotransferase mRNA activity. These studies demonstrate that, in intact animals, the induction of tyrosine aminotransferase activity by dibutyryl cyclic AMP can be completely accounted for by a corresponding increase in the level of functional mRNA coding for the enzyme.     

Evaluation of key gluconeogenic enzymes in experimental biliary obstruction

In order to evaluate the usefulness of key gluconeogenic enzymes, in relation to the markers commonly used (alkaline phosphatase and gamma-glutamyl transpeptidase) for the diagnose of cholestasis the serum activity of phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase and glucose-6-phosphatase has been measured in rats with bile-duct ligation. Among the gluconeogenic enzymes studied only phosphoenolpyruvate carboxykinase activity increased significantly in the first 48 hours after cholestasis, decreasing thereafter to normal values. Both alkaline phosphatase and gamma-glutamyl transpeptidase activities showed a very significant increase which persisted throughout the experiment. These results seem to indicate that in spite of the high organ specificity of these enzymes they do not appear to be useful for the diagnosis of cholestasis.     

Hepatic cyclic AMP generation and ornithine decarboxylase induction by glucagon and beta adrenergic agonists

The relationship of hepatic ornithine decarboxylase (ODC) activity to cyclic AMP levels and nutritional status was studied in the pre-weanling rat. Previous studies demonstrated that 2 hr without food causes a loss of hepatic ODC induction after glucagon or catecholamine injection. Isoproterenol or glucagon administration produced increased hepatic cyclic AMP and tyrosine aminotransferase activity which were not prevented by nutritional deprivation. Blockade of hepatic beta 2 receptors by the selective antagonist ICI 118,551 prevented increased cAMP levels and ODC activity after isoproterenol administration. Blockade of beta 1 receptors by atenolol did not prevent increased cAMP levels or ODC induction by isoproterenol although it did block activation of cardiac ODC. The phosphodiesterase inhibitor RO20-1724 increased hepatic cAMP levels as well as ODC and TAT activities, although the increase in ODC activity was attenuated by nutritional deprivation. RO20-1724 also potentiated the induction of hepatic ODC after glucagon or isoproterenol administration. Administration of 8-bromo cAMP elevated hepatic ODC activity regardless of nutritional status but also elevated serum levels of growth hormone and corticosterone. Hepatic ODC induction by glucagon or beta 2 agonists can be dissociated from changes in cAMP levels during nutritional deprivation.     

The inhibition by xanthine phosphodiesterase inhibitors of the induction of alkaline phosphatase activity in HeLa cells: relationship of enzyme activity to cyclic AMP concentrations.

The three xanthine derivatives, caffeine, theophylline and 3-isobutyl-1-methyl-xanthine (IBMX) produced dose-dependent increases in cyclic AMP concentrations in HeLa cells after long term treatment. Only IBMX produced increases over the first 60 minutes, with a peak of approximately 5-fold control values five to 10 minutes after the addition of the drug. About four hours after the addition of either 0.67 or 1.0 mM IBMX there was a second peak in the concentration of cyclic AMP which was at least as large and usually larger than the peak observed at five to ten minutes. Neither caffeine nor theophylline increased cyclic AMP concentrations above control values until one hour after addition of the compounds, and there was no indication of a peak in the concentration at four hours. Between 24 and 72 hours, all three compounds produced elevations in cyclic AMP levels that were steadily maintained. At any given concentration, the order of potency was IBMX greater than theophylline greater than caffeine. If the xanthine derivatives were removed from the medium after 24 hours of treatment, the cyclic AMP concentrations fell to control levels within one hour. Treatment with 5-iodo-2'-deoxyuridine (IdUrd) or hydrocortisone alone did not change the levels of cyclic AMP, nor did the presence of these inducers of alkaline phosphatase activity alter the effects of the xanthine derivations on cyclic AMP concentrations. The data showed a significant correlation between the magnitude of the increase in cycli AMP concentrations over the period from 24 to 72 hours and the degree of inhibition by the xanthine derivatives of the induction of alkaline phosphatase activity.     

Induction of alkaline phosphatase in choriocarcinoma cells by 1-beta-D-arabinofuranosyl-cytosine, mitomycin C, phleomycin, and cyclic nucleotides.

Alkaline phosphatase is induced in cultured human choriocarcinoma cells by three inhibitors of DNA synthesis which alter DNA structure: 1-β-D-arabinofuranosyl-cytosine, mitomycin C, and phleomycin. No induction is observed with the inhibitors, hydroxyurea and thymidine, which do not alter DNA structure. Cyclic AMP, analogs of cyclic nucleotides, and sodium butyrate also induce alkaline phosphatase in these cells. Among the cyclic nucleotides tested, dibutyryl cyclic AMP is the best inducer, whereas dibutyryl cyclic GMP is a poor inducer. Induction of alkaline phosphatase by inhibitors of DNA synthesis or by exposure to dibutyryl cyclic AMP appears to utilize different mechanisms. Maximum induction is observed after simultaneous addition of both types of inducers at the concentrations found to be optimal for each inducer alone. Under these conditions, the induced activity is equal to or greater than the sum of the activities induced by each inducer. RNA synthesis and protein synthesis are required for induction. Dibutyryl cyclic AMP added to cultures of choriocarcinoma cells is not degraded in the culture medium, but is extensively degraded in the cells. Nevertheless, significant amounts of dibutyryl and monobutyryl cyclic AMP are found intracellularly throughout the experiment. Since the cellular uptake of dibutyryl cyclic AMP is extremely slow, the amount of butyrate released by intracellular degradation cannot account for the observed induction. Neither the rate of uptake nor the stability of dibutyryl cyclic AMP are changed by the addition of 1-β-D-arabinofuranosyl-cytosine to the culture medium. Furthermore, 1-β-D-arabinofuranosyl-cytosine inhibits the induction by sodium butyrate. The results indicate that butyrate is not the major mediator of induction by dibutyryl cyclic AMP.     

Induction of Rat Liver Alkaline Phosphatase by Bile Duct Ligation

Bile duct ligation causes a five- to sevenfold increase in the activity of rat liver alkaline phosphatase within 12 hours after ligation and a similar rise in the activity of alkaline phosphatase in serum. The increased serum activity is due entirely to the appearance of a new isoenzyme that has the properties of rat liver alkaline phosphatase. The increase in both serum and liver alkaline phosphatase is prevented by the prior administration of cycloheximide in a dose that inhibits protein synthesis by 70%. Rat liver alkaline phosphatase was then purified to homogeneity. Antibody was raised to purified rat liver alkaline phosphatase in rabbits. The antibody was coupled to sepharose 4B and affinity columns made. ³-H-leucine was then injected into the portal veins of sham operated rats and rats with bile duct ligation four hours after ligation. One hour after injection and five hours after ligation, animals were sacrificed. Liver alkaline phosphatase was purified by means of affinity chromatography and double immunoprecipitation with rabbit antibody to rat liver alkaline phosphatase and goat anti-rabbit gamma globulin. Bile duct ligation increased the incorporation of ³-H-leucine into liver alkaline phosphatase more than threefold compared with sham operated rats, 164 CPM/mg protein vs. 49 CPM/mg protein (p < .001). The data indicate that the increased activity of rat liver alkaline phosphatase after bile duct ligation is due to enzyme induction rather than to activation of a pre-existing, relatively inactive enzyme.     

The response of alkaline phosphatase to osmoregulatory changes in the trout,Salmo gairdneri

Summary The relationship between alkaline phosphatase and environmental salinity was examined in the rainbow trout and the migratory rainbow (steelhead),Salmo gairdneri. The enzyme activity in tissues involved in osmoregulation was strongly correlated with the adaptation salinity and thus to the degree of salt and fluid transport in those tissues. After transfer from freshwater to seawater, the specific activity of the enzyme increased over 260% in the intestine, decreased by 50% in kidney, and was unchanged in the liver, an organ not directly involved in osmoregulation. The sea-run steelhead trout response was similar to the nonmigratory rainbow; although, the pre-migratory transformation (smoltification) had no effect on enzyme activity. Amino acid inhibitors of alkaline phosphatase significantly reduced fluid absorption in the isolated intestine of rainbow trout, reaffirming the relationship between the enzyme and fluid movement. Electrophoretic identification of trout alkaline phosphatase isozymes, clearly distinguishes the enzyme from different tissue origins. However, from the analysis of intestinal electrophoretic patterns, osmoregulatory adjustments are not associated with the induction of new alkaline phosphatase isozymes, or in the large scale preferential stimulation of one of the two existing intestinal isozymes over the other.     

Hormonal regulation of fatty acid synthetase in chick embryo liver.

Fatty acid synthetase activity in chick embryonic liver is negligible compared to that in newly hatched, fed chicks. The enzyme activity is prematurely induced 5–50-fold in 20-day-old embryos and in newly hatched chicks by the administration of insulin, hydrocortisone, growth hormone, glucagon or dibutyryl cyclic AMP. The induction of the enzyme activity is blocked by the administration of cycloheximide, indicating that new protein synthesis is required. Immunochemical titrations of different enzyme preparations from 5-day-old chicks, adult chicken and various inducer-treated embryos gave an identical equivalence point, indicating that the changes in synthetase activity after hormonal induction in embryos are related entirely to changes in content of enzyme. The increase in liver synthetase content after administration of insulin, glucagon or dibutyryl cyclic AMP is directly related to an increase in the rate of synthetase synthesis. The induction of the synthetase activity by suboptimal doses of glucagon or cyclic AMP is potentiated by the phosphodiesterase inhibitory theophylline. There is a very rapid decay of synthetase activity, with a half-life of about 4 h after elevation to higher levels following administration of insulin, glucagon or dibutyryl cyclic AMP. Glucagon and dibutyryl cyclic AMP induction of the synthetase activity is observed early in the embryonic development, whereas insulin induction is noted 2 days before hatching. Insulin, glucagon and cyclic AMP are potentially capable of altering the levels of glycolytic intermediates which may be involved in the induction of synthetase.     

Induction of alkaline phosphatase activity in HeLa cells by sodium butyrate.

The induction of HeLa cell alkaline phosphatase activity by sodium butyrate could be inhibited by the coadministration of caffeine or theophylline. The inhibitions were dose dependent, and at any given concentration the potency was theophylline greater than caffeine. Although the induction by sodium butyrate was more sensitive to the inhibition by the xanthines than was that produced by 5-iodo-2'-deoxyuridine, the magnitudes of the increases in cyclic AMP concentrations after treatment with the xanthines were similar in the inhibition of both types of induction. The induction of alkaline phosphatase activity by sodium butyrate also produced a shift in the thermostability pattern of the enzyme, with a proportionately greater increase in the heat-labile, rather than heat-stable, form of the activity.     

Induction of alkaline phosphatase in cultured human fibroblasts. Comparison of normal cells and those from patients with cystic fibrosis.

The membrane glycoprotein enzyme, alkaline phosphatase was induced in cultured human fibroblasts by dibutyryl cyclic AMP, sodium butyrate, the serum glycoprotein fetuin, the Tamm-Horsfall urinary glycoprotein, and by a number of inhibitors of DNA synthesis. The uninduced basal enzyme activity increased at later stages of growth when the cells became confluent. Induction by dibutyryl cyclic AMP or fetuin was most effective when the agents were added after the cells had reached stationary phase and was maximal after at least two days of exposure. The levels of induction resulting from the addition of pairs of the agents, dibutyryl cyclic AMP, n-butyrate and fetuin were additive indicating that these have different modes of action. The inhibitors of DNA synthesis, cytosine arabinoside, hydroxyurea, and methothrexate were less effective inducers. Bromodeoxyuridine which also has non-DNA mediated effects induced to the same extent as dibutyryl cyclic AMP. Similar experiments with sex- and age-matched cell strains derived from patients with cystic fibrosis failed to detect differences in the levels of induction from those observed in normal cells. In addition, the combined inductive effects of Tamm-Horsfall glycoprotein, isoproterenol and theophylline, were similar with normal and cystic fibrosis cells.