Increase In Hexokinase Activity Research Articles

Control of glucose metabolism in newborn pig enterocytes: Evidence for the role of hexokinase

The objective of the present work was to identify the regulatory step(s) in the post-natal development of a high glycolytic capacity previously evidenced in newborn pig enterocytes (Darcy-Vrillon et al. (1994) Pediat. Res., 36, 175–181. Glucose entry via the Na + glucose cotransporter, estimated by the uptake of the non-metabolizable analogue methyl α- d-[U- 14C]glucopyranoside, slightly decreased between birth and 2 days of sucking. The flux of glucose metabolized into the pentose cycle pathway slightly increased but could not account for the 3-fold increase observed in the glycolytic capacity. Whereas the maximal activity of 6-phosphofructo-1-kinase did not change between stages, there was a significant increase in hexokinase activity as well as in the flux of glucose phosphorylated. These findings suggest that the stimulation of glucose phosphorylation through hexokinase is the key event leading to an increased glycolytic capacity of small intestinal cells at the onset of sucking.

Protective Action of Succinic Acid Monomethyl Ester Against the Impairment of Glucose-Stimulated Insulin Release Caused by Glucopenia or Starvation: Metabolic Determinants

The monomethyl ester of succinic acid (SME) was recently found to protect pancreatic islet B-cells against the impairment of glucose-stimulated insulin release caused by either glucopenia or starvation. The possible metabolic determinants of such a protective action are now scrutinized. After 180 min preincubation at 2.8 mM D-glucose in the presence of SME (10 mM), the oxidation of D-[U-14C]glucose, relative to either the utilization of D-[5-3H]glucose or the generation of 14C-labeled acidic metabolites, was higher than that after preincubation in the absence of SME and became close to that otherwise found after preincubation at 16.7 mM D-glucose. Likewise, after 3 days of culture at a low concentration of D-glucose (2.8 mM), the presence of SME in the culture medium tended to increase the subsequent oxidation of D-[6-14C]glucose and utilization of D-[5-3H]glucose. These two variables increased as a function of the concentration of D-glucose in the culture medium, this coinciding with a modest increase in hexokinase activity and a more pronounced increase in glucokinase activity. The presence of SME in the culture medium failed, however, to exert any obvious effect upon the respiration of the islets, suggesting that the protective action of the ester against glucopenia may also involve variables distinct from the metabolism of either endogenous or exogenous nutrients. Likewise, the fact that SME infusion to starved rats prevents the impairment of glucose-induced insulin release otherwise attributable to starvation may involve enzymatic determinants, such as a less severe decrease in glucokinase activity, metabolic variables, such as a greater relative increase in D-[U-14C]glucose oxidation relative to D-[5-3H]glucose utilization in response to a rise in extracellular D-glucose concentration, and other factors yet to be identified that participate in the secretory sequence at a site distal to those metabolic events triggered by D-glucose in the islet cells.

Overexpression of hexokinase I in isolated islets of Langerhans via recombinant adenovirus. Enhancement of glucose metabolism and insulin secretion at basal but not stimulatory glucose levels.

Glucose metabolism and glucose-stimulated insulin secretion are thought to be controlled at the level of glucose phosphorylation in pancreatic islet beta-cells. In the current study we have investigated the importance of glucose phosphorylation by using recombinant adenovirus as a gene delivery system for isolated rat islets. Treatment of islets with a virus containing the cDNA encoding the Escherichia coli beta-galactosidase gene (AdCMV-beta GAL) resulted in efficiencies of gene transfer of 70.3 +/- 2.5 and 61.2 +/- 2.2% in two independent experiments. Treatment of islets with a virus containing the cDNA encoding rat hexokinase I (AdCMV-HKI) resulted in a 10.7-fold increase in immunodetectable hexokinase protein and a similar increase in enzyme activity. A large percentage of the overexpressed hexokinase activity was associated with a cell fraction enriched in mitochondria. These changes in enzyme level were accompanied by a 2-fold increase in insulin release and [5-3H]glucose usage at basal glucose concentrations (3 mM). The rate of glucose usage at 20 mM glucose and the magnitude of the insulin secretory response to this stimulatory level of the sugar were unchanged relative to control islets. Overexpression of hexokinase I in isolated islets therefore creates a phenotype of elevated basal insulin release similar to that seen in islets from obese and insulin-resistant mammals. The discrepancy between the large increase in hexokinase activity and the small increase in glucose usage and insulin release may indicate, however, that other steps in glucose metabolism become rate-limiting after only modest increases in glucose-phosphorylating activity.

Rapid Eye Movement Sleep-Deprivation-Induced Changes in Glucose Metabolic Enzymes in Rat Brain

Glucose metabolism and energy expenditure are altered during rapid eye movement (REM) sleep. To understand this mechanism, it was hypothesized that the enzymes involved in the metabolism of glucose, viz. hexokinase and glucose-6-phosphatase, are affected by REM sleep deprivation. The flower pot technique was used for 1-, 2- and 4-day periods of REM sleep deprivation. Suitable control experiments were carried out to rule out the nonspecific effects. The results showed that glucose-6-phosphatase was first to be affected, and it showed decreased activity. In longer periods of deprivation, there was an increase in hexokinase activity. Both the altered enzyme activities returned to baseline level on recovery from REM sleep deprivation. Control experiments suggest that alterations were primarily caused by REM sleep deprivation, not nonspecific effects.

Alterations in brain hexokinase activity associated with heart failure in rats.

This study examined the activity of discrete regions of the brain as assessed with histological localization and photodensitometric quantification of the metabolic enzyme hexokinase in a group of rats with coronary occlusion (HF) and in sham-operated control rats. Three weeks after surgery, the mean left ventricular end diastolic pressure and right atrial pressure were elevated, and left ventricular peak systolic pressure was decreased in the HF group compared with the sham group; these findings are also observed during heart failure. In addition, histological data indicated that there was a 37.6 +/- 2.8% outer and 40.8 +/- 3.1% inner infarct of the myocardium in the group of rats with HF (n = 6). Rats in the control group had no observable damage to the myocardium (n = 6). Accompanying these symptoms of heart failure were significant increases in hexokinase activity in the parvocellular (pPVN, 16.3%) and magnocellular (mPVN, 17.6%) divisions of the paraventricular nucleus of the hypothalamus, and in the locus ceruleus (LC, 17.1%). No changes in hexokinase activity were observed in the median preoptic area, supraoptic nucleus (SON), subfornical organ, or posterior hypothalamus. These results reinforce the idea that heart failure (with coronary occlusion) is associated with changes in specific areas in the brain and that metabolic alterations in the pPVN, mPVN, and LC are likely related to alterations in vasopressin production, blood volume regulation, and sympathoexcitation observed in the heart failure state.

Murine Insulinoma Cell Line With Normal Glucose-Regulated Insulin Secretion

Pancreatic beta TC lines derived from insulinomas arising in transgenic mice expressing SV40 Tag under control of the insulin promoter manifest a differentiated beta-cell phenotype and secrete insulin in response to glucose. Previously reported beta TC lines respond to subphysiological extracellular glucose levels compared with normal beta-cells. Recently, several beta TC lines were developed with normal glucose-regulated insulin secretion from insulinomas obtained by breeding of the RIP-Tag transgene from the original C57BI/6 mouse strain into the C3HeB/FeJ strain. One of these beta TC lines, beta TC7, was characterized in detail. Beta TC7 cells express GLUT2 and have levels of glucokinase and hexokinase activity similar to those of normal islets. As a result these cells exhibit a normal glucose concentration dependency for glycolysis and insulin secretion, thus representing an accurate model of beta-cell function. On continuous propagation in culture, beta TC7 cells acquired a response to lower extracellular glucose levels. This change was associated with a fourfold increase in hexokinase activity, without significant changes in glucokinase activity and glucose uptake rates. These findings suggest an important role for glucose phosphorylation rates in regulation of the beta-cell insulin secretory response to glucose.

Regulation of Glucose Metabolism in Livers and Kidneys of NOD Mice

Measurements were made of the levels of metabolic intermediates and activities of enzymes of the glycolytic route, pentose phosphate pathway, and polyol pathway in livers and kidneys of NOD mice. A 34% decrease in UDP-glucose, a 40% decrease in glucose-6-phosphate (G6P) and fructose-6-phosphate, and a 75% decrease in fructose-2,6-bisphosphate (F2,6P) were found in the livers of NOD mice. The fall in the level of F2,6P (the important regulator of glycolysis) is accompanied by a 20% reduction in the activity of phosphofructokinase. These changes are in agreement with previously reported liver depletion of glycogen and reduced synthesis of proteins and nucleic acids in the diabetic state. In the kidney, the increase in hexokinase activity is consistent with increased levels of G6P and glycogen content of kidney in diabetes. The decreased level of phosphoribosyl pyrophosphate was reported to be a regulator of kidney growth in the initial period of diabetes but can still be found in NOD mice 6 wk after development of hyperglycemia. The reported changes are similar to those seen in alloxan- or streptozocin-induced diabetic animals, but certain changes are more marked in NOD mice, especially those directed to increase nucleic acid and protein synthesis in the diabetic kidney.

Changes in free and bound forms and total amount of hexokinase isozyme II of rat muscle in response to contractile activity

Increased contractile activity as induced by chronic low-frequency stimulation evoked in rat fast-twitch muscle an almost immediate increase in the ratio between structure-bound and free hexokinase. In addition, an up to 14-fold rise in total hexokinase activity occurred after two weeks of stimulation indicating that glucose phosphorylation became a limiting step of glucose utilization under these conditions. The increase in hexokinase activity was transitory as prolonged stimulation led to a leveling off and steep decline with an apparent half-life of 2.5 days after three weeks of stimulation. The transient increase in glucose phosphorylating capacity can be explained by previous observations indicating that prolonged stimulation leads to a shift from a carbohydrate-based to a fatty-acid-based energy metabolism. Using an isozyme-specific sandwich ELISA, it was shown that both increases and decreases in total hexokinase activity were matched by corresponding changes in the amount of hexokinase isozyme II protein. Increases in both total hexokinase activity (3-4-fold) and hexokinase II protein content were also observed after denervation in rat fast-twitch muscle. In view of reports in the literature, it is suggested that the elevations in hexokinase II observed with increased contractile activity and denervation relate to enhanced glucose uptake and utilization.

Alterations in brain hexokinase activity associated with streptozoticin-induced diabetes mellitus in the rat

The effects of streptozotocin-induced diabetes mellitus on the activity of discrete regions of the brain were studied with histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase. Two weeks after a single injection of streptozotocin (65 mg/kg, i.p.), plasma glucose and osmolarity levels were elevated, and plasma sodium concentrations were depressed. These changes were reversed in diabetic rats treated with insulin. Accompanying these symptoms of diabetes were significant increases in hexokinase activity in the magnocellular division of the paraventricular nucleus of the hypothalamus (mPVH, 1`2.1%), the medial subdivision of the nucleus of the tractus solitarius (mNTS, 15.5%), and the commissural subdivision of the NTS (cNTS, 10.9%). An increase, though just below the level of significance, was also observed in the supraoptic nucleus of the hypothalamus (SON, 11.5%). The increases in hexokinase activity were completely reversed in the cNTS (and SON) and only partly reversed in the mPVH and mNTS of insulin-treated diabetic rats. No changes in hexokinase activity were seen in the subfornical organ, medial preoptic area, parvocellular division of the PVH, locus coeruleus, or dorsal motor nucleus of the vagus of diabetic rats. These results reinforce the idea that the brain is not exempt from changes associated with diabetes mellitus and suggest that metabolic alterations in the mPVH (and SON) and two divisions of the NTS are likely related to changes in vasopressin production and blood volume, respectively.

Renal denervation alters forebrain hexokinase activity in neurogenic hypertensive rats.

The effect of afferent renal nerve transection (tARN) on the metabolic activity of forebrain structures the activity of which was altered after aortic depressor nerve transection (tADN) was studied using the hexokinase (HK) histochemical method in the rat. In tADN-sham (s) ARN rats, increases in HK activity were observed in the medial septum (MS), median preoptic nucleus (MnPO), subfornical organ, supraoptic nucleus, nucleus circularis (Nc), magnocellular, and dorsal and medial (mpPVH) parvocellular components of paraventricular nucleus, the anterior, lateral, and dorsomedial (DMH) hypothalamus, and in the central and medial nuclei of the amygdala. In addition, a decrease in HK activity was seen in the dorsal arcuate nucleus (dArc). Similarly, increases in HK activity were seen in sADN-tARN rats in all the above structures except MS, Nc, and DMH, where no changes were observed, and dArc, where an increase in HK activity was noted. The bed nucleus of the stria terminalis, lateral preoptic nucleus (POA), and ventral (v) Arc also showed elevated HK activity. In contrast, the increased HK activity after either tADN or tARN alone was returned to levels not different from sADN-sARN rats in all structures in the tADN-tARN rats, except MnPO, mpPVH, and dArc, where the level of HK activity was only attenuated, and MS, POA, and vArc, where it remained elevated. These data suggest that similar forebrain structure are associated with the hypertension after tADN and are involved in the integration of ARN information and that these sites of interaction are involved in the maintenance and the reversal of the neurogenic hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Low-Iodine Diet and Propylthiouracil on Glycolytic Enzymes in Brain Areas of Adult Rats

Glycolytic activity of five brain areas in the rat was studied under two hypothyroid states: (1) induced by low-iodine diet from weaning, and (2) induced by propylthiouracil. The areas studied were the anterior cortex, amygdala, hypothalamus, septum and hippocampus. A low-iodine diet induced a decrease of pyruvate kinase activity in three region and of phosphofructokinase in the hippocampus, while hexokinase increased in both the amygdala and septum. Propylthiouracil treatment produced an increase in hexokinase activity in the hypothalamus and septum, and a decrease in the anterior cortex, while phosphofructokinase decreased significantly in the hippocampus. No significant changes of lactate dehydrogenase activity were observed. The correlation between the results and type of hypothyroidism is discussed.

Contractile activity enhances the synthesis of hexokinase II in rat skeletal muscle

An 11-fold increase in hexokinase activity and the hexokinase II isoform was found in rat tibialis anterior muscle after 7 days of chronic, low-frequency stimulation. In vivo labeling studies showed that this increase in enzyme protein content was related to an approx. 30-fold increase in [ 35S]methionine incorporation.

Effect of phorbol myristate acetate and concanavalin A on the glycolytic enzymes of human peripheral lymphocytes

The effects of Concanavalin A and the tumor promoting agent, phorbol 12-myristate 13-acetate (PMA), on glycolytic enzymes in human peripheral lymphocytes have been studied. A combination of Concanavalin A plus PMA stimulates DNA and protein synthesis to a significantly greater extent than when each are added individually. PMA and concanavalin A together, but not individually, also increase the levels of the activity of the glycolytic enzymes in peripheral lymphocytes treated for 48 h. The increase in hexokinase activity induced by PMA plus concanavalin A appeared to be due to the expression of the isoenzyme form, hexokinase II. The results suggest that the expression of glycolytic enzymes in stimulated lymphocytes is a late event (perhaps associated with the S phase) which is regulated by a cellular signal system controlled by the combined action of PMA plus concanavalin A.

Increased hexokinase activity in forebrain of water-deprived and diabetes insipidus rats.

Metabolic studies using the 2-[14C]deoxy-D-glucose and cytochrome oxidase techniques have demonstrated changes in the activity of central sites associated with the hypothalamoneurohypophysial system in water-deprived (WD) and diabetes insipidus (DI) rats. Another method that may be used as an index of metabolic activity in discrete regions of the central nervous system is the measurement of hexokinase (HK) activity. This study describes changes in metabolic activity, as measured by HK histochemistry, in regions of the forebrain of WD and DI rats. Significant increases in HK activity measured by densitometric analysis were observed in the magnocellular component of the paraventricular nucleus of the hypothalamus, supraoptic nucleus, nucleus circularis, and neurohypophysis of WD and DI rats. In addition, increased HK activity was observed in the preoptic area and subfornical organ of DI rats. These data demonstrate that metabolic changes occur in the forebrain of WD and DI rats within structures involved in body fluid regulation. The present study also demonstrates that HK histochemistry may be used as a marker of metabolic activity in discrete regions of the central nervous system.

Changes in forebrain hexokinase activity after aortic baroreceptor denervation.

Although forebrain structures have been implicated in both the development and maintenance of the elevated arterial pressure (AP) after aortic baroreceptor denervation, little is known about the location of central structures involved in the hypertensive process. In the present study, regions of the forebrain whose metabolic activity was altered after aortic baroreceptor denervation were functionally identified using hexokinase (HK) histochemistry in the rat. Three days after bilateral aortic depressor nerve (ADN) transection AP was significantly elevated compared with sham ADN-transected animals (143 +/- 1 and 122 +/- 2 mmHg, respectively). Significant increases in HK activity were observed in the magno- and parvocellular components of the paraventricular nucleus of the hypothalamus, supraoptic nucleus, nucleus circularis, median preoptic nucleus, subfornical organ, and central nucleus of the amygdala in the ADN-transected animals. These data have demonstrated that removal of aortic baroreceptor afferent inputs alters the activity of forebrain structures previously implicated in regulation of body fluid balance and AP and suggest that these structures are involved in the hypertensive process after ADN transection.

Effect of hyperthyroidism on fibre-type composition, fibre area, glycogen content and enzyme activity in human skeletal muscle.

Seven hyperthyroid patients were studied by repeated muscle biopsies (vastus lateralis) before and after a period of medical treatment which averaged 10 months. The biopsies were analysed with regard to fibre-type composition, fibre area, capillary density, glycogen content and enzyme activities representing the glycolytic capacity (hexokinase, 6-phosphofructokinase), oxidative capacity (oxoglutarate dehydrogenase, citrate synthase) and Ca2+- and Mg2+-stimulated ATPase in muscle. In the pretreatment biopsy (hyperthyroid state), there was a significantly lower proportion of type I fibres (30% vs. 41%), a higher capillary density (23%), lower glycogen content (33%), and higher hexokinase activity (32%) compared with the post-treatment biopsy. No significant changes in the activity of the remaining enzymes were observed. The present study indicates that hyperthyroidism induces a transformation from type I to type II fibres in human skeletal muscle. The increase in hexokinase activity probably reflects a higher glucose utilization by skeletal muscle in order to compensate partially for the reduced glycogen content.

Reduced maximum capacity of glycolysis in brown adipose tissue of genetically obese, diabetic (db/db) mice and its restoration following treatment with a thermogenic β-adrenoceptor agonist

The maximal activities of the key glycolytic enzymes hexokinase and 6-phosphofructokinase, were reduced in brown adipose tissue in db/db mice compared to their lean littermates. Treatment of db/db mice with the thermogenic β-adrenoceptor agonist, BRL 26830, restored normoglycaemia. The only significant increase in activity of hexokinase and 6-phosphofructokinase in the BRL 26830-treated db/db mice occurred in brown adipose tissue where the total tissue activity increased 10- and 11-fold respectively. These changes together with increased 2-deoxyglucose uptake in vivo suggest that brown adipose tissue can play a quantitatively important role in the removal of glucose from the blood.

Relationship between erythrocyte hexokinase in cancer patients and red cell age.

A study of hexokinase isozymic pattern and age dependence of the enzyme was carried out on erythrocytes of 4 patients with adenocarcinoma of the gastrointestinal tract. On the basis of our results, we think that the increase in hexokinase activity previously reported and the increase in both subtypes (Ia and Ib) of the enzyme herein described are not due to a mean younger red cell population caused by secondary anemia, which is frequently present in cancer patients.

Kinetic models of glycogen metabolism in normal rat liver, morris Hepatom 7787 and host liver

1. 1. Consistent with data on metabolite concentration and flux, kinetic models have been constructed for normal rat liver, well differentiated Hepatoma 7787 and host liver. 2. 2. To mimic the experimental conditions (feeding), an external flux of glucose was imposed on the models in order to produce the metabolite accumulation patterns observed. 3. 3. Glycogen synthetase is the critical enzyme which it is both necessary and sufficient to perturb in order to change the model of normal liver into the models of host liver and Hepatoma 7787. 4. 4. A decrease of 12-fold and 62-fold, respectively, in the activity of this enzyme gives output simulating the data for host liver and Hepatoma 7787. 5. 5. Such a decreased activity of glycogen synthetase in the hepatoma model is consistent with the literature. 6. 6. However, other changes have also been observed in this and other slowly growing tumors: (a) a decrease in glucokinase activity and an increase in hexokinase activity: (b) a lack of response of glycogen levels to feeding; (c) an increase in glucose-6-phosphate dehydrogenase activity and (d) a decrease in glycogen phosphorylase activity. 7. 7. Incorporation of the first three changes in the hepatoma model made remarkably little difference in the output. However, the rate of glycogen degradation, catalyzed by glycogen phosphorylase, must remain unchanged (assuming a 3-fold increase in glycogen levels on feeding) or be increased 50-fold (assuming no response to feeding). 8. 8. Hence, the flux of glycogen degradation appears to be the same or higher in the hepatoma as compared to normal liver.

The increase in hexokinase activity in heredityry avian muscular dystrophy

Hexokinase activity was found to be increased in both the more severely affected white (pectoral) and less severely affected red (thigh) muscle of dystrophic chickens. The increase in activity was largely associated with the particulate fraction. These findings may indicate early events in the pathogenesis of avian muscular dystrophy.