Glycogen metabolizing enzymes in brain

Three enzymes, glycogen phosphorylase, glycogen synthase, and phosphoglucomutase were evaluated in subcellular fractions and in brain regions. Also the development of each of these enzymes was evaluated in whole brain homogenates. Each enzyme increased during the first three weeks of post partum in a manner that is similar to the development of glycolytic enzymes during this period. The specific activity of each enzyme in various subcellular fractions indicated that the enzymes were primarily soluble. Also unlike the glycolytic enzyme phosphoglycerate kinase, the glycogen metabolizing enzymes had a lower specific activity in synaptosomes than in particle free supernatant fractions of homogenates. Regarding regional distribution small (less than twofold) but significant differences were seen between different brain areas. An inverse relationship between the glycogen metabolizing enzymes and hexokinase was observed, that is, regions highest in glycogen synthase and glycogen phosphorylase were lowest in hexokinase and regions highest in hexokinase were lowest in the glycogen metabolizing enzymes.     

Effect of undernutrition on some enzymes involved in the salvage pathway of purine nucleotides in different regions of developing rat brain

The effect of undernutrition on the activity of two key enzymes of purine salvage pathway, namely hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) and adenine phosphoribosyltransferase (APRTase), in cerebral hemispheres, cerebellum and brain stem of rats at different days of postnatal development was studied. The activity of HGPRTase and of APRTase is significantly lower in all brain regions of undernourished animals at 5 days after birth; between 10 and 15 days of age there is a recovery of the enzymatic activity which is particularly evident in the cerebellum. Successively both enzymatic activities decrease reaching at 30 days of age values quite similar to those of controls. These results indicate that undernutrition during fetal and postnatal development, impairs and delays the activity of the enzymes of purine salvage pathway.     

Response of hepatic fructokinase to long-term sucrose diets and diabetes in spiny mice, albino mice and rats

The activity of hepatic fructokinase increased about 2-fold in desert-derived spiny mice (Acomys cahirinus) and laboratory bred albino mice and rats, maintained on a 50% sucrose diet for 3 months. The role of fructose as the specific inducer was apparent, as 25% fructose diet produced activity increases similar to those of sucrose in contrast to 25% glucose diet. The activity of hexokinase was not affected by the sucrose diet, that of glucokinase rose marginally but those of pyruvate kinase and NADP-malate dehydrogenase rose pronouncedly, especially in the spiny mice. Fructokinase activity increased significantly only after 2 weeks on the diet and continued to rise gradually. The activities of other gycolytic enzymes rose markedly already after 3 days and peaked at about 14 days. Fasting for 48 hr did not influence fructokinase activity while markedly reducing that of glucokinase, pyruvate kinase and NADP-malate dehydrogenase. Streptozotocin diabetes in rats resulted in a 40% reduction in fructokinase activity after 14 days which was restored after 6 days of insulin treatment. The activity increases of other glycolytic enzymes were more marked. However, the fructokinase induction on the sucrose diet was evident also in diabetic rats, suggesting that the insulin and substrate effects are independent. The preference of fructose over glucose phosphorylation capacity was clearly demonstrable in the non-diabetic and diabetic rats and became enhanced on sucrose feeding. The activity of triokinase also increased on the sucrose diet in the 3 rodent species, suggesting a coordinative substrate effect on the induction of these two rate-limiting fructolysis enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in the distribution of energy-metabolizing enzymes in rat brain regions

The activities of several enzymes of glucose metabolism (glycolytic and tricarboxylic acid pathways) in four different regions of rat brain (cerebellum, medulla oblongata and pons, cerebral cortex and diencephalon) have been studied. Statistical differences were found in the activities of all the enzymes analyzed in the four regions, except in the case of the soluble hexokinase and pyruvate kinase. The changes observed in citrate synthase activity may account for physiological differences in those areas related to myelin formation and energy metabolism. Cerebral cortex and diencephalon showed enzyme activities which were generally greater than those of the cerebellum and medulla oblongata and pons. The results obtained lend support to the concept of a differential energy metabolism in brain regions.     

Region specific increase in the antioxidant enzymes and lipid peroxidation products in the brain of rats exposed to lead

The objective of this study is to determine the effect of lead (pb) on antioxidant enzymes and lipid peroxidation products in different regions of rat brain. Wistar male rats were treated with lead acetate (500 ppm) through drinking water for a period of 8 weeks. Control animals were maintained on sodium acetate. Treated and control rats were sacrificed at intervals of 1st, 4th and 8th week and the whole brains were dissected on ice into four regions namely the cerebellum, the hippocampus, the frontal cortex and the brain stem. Antioxidant enzymes namely catalase and superoxide dismutase in all the four regions of brain were determined. In addition, lipid peroxidation products were also estimated. The results indicated a gradual increase in the activity of antioxidant enzymes in different regions of the brain and this response was time-dependent. However, the increase was more in the cerebellum and the hippocampus compared to other regions of the brain. The lipid peroxidation products also showed a similar trend suggesting increased effect of lead in these two regions of the brain. The data indicated a region-specific oxidative stress in the brain exposed to lead.     

Changes in Monoamine Oxidase Activity in Rat Brain During Alloxan Diabetes

Abstract: The effect of alloxan diabetes on the activity of monoamine oxidase was studied in three regions of the rat brain at various time intervals after the onset of diabetes. It was observed that monoamine oxidase activity was decreased at early time intervals after diabetes, followed by a recovery in all three regions of the brain. A reversal of the effect was observed with insulin administration to the diabetic rats.     

Changes in glucose metabolism from discrete regions of rat brain and its relationship to reproductive failure during experimental diabetes

This study reports the effects of alloxan induced diabetes on glucose metabolism enzymes viz. Hexokinase, Lactate dehydrogenase, and Glucose-6-phosphate dehydrogenase from discrete brain regions. Enzymes activity was assayed from hypothalamic areas such as medial preoptic area and median eminence-arcuate region which have gonadotropin releasing hormone cell bodies and their terminals, respectively and other brain regions like septum, amygdala, hippocampus, and thalamus. In all the areas studied, induction of diabetes resulted in a significant decrease in particulate bound HK activity, whereas soluble HK, LDH and G6PDH activity showed increase at 3, 8, 15 and 28 days intervals. Insulin treatment of diabetic rats led to recovery in enzyme activity. Blood glucose levels increased significantly after induction of diabetes and recovery was seen after insulin treatment. The present results suggest that altered cerebral glucose metabolism may also be responsible for reproductive failure observed in diabetic rats. (Mol Cell Biochem141: 97–102, 1994)     

Trigonella foenum graecum (fenugreek) seed powder improves glucose homeostasis in alloxan diabetic rat tissues by reversing the altered glycolytic,gluconeogenic and lipogenic enzymes

Trigonella foenum graecum (fenugreek) seed powder has been suggested to have potential antidiabetic effects. The effect of oral administration of Trigonella whole seed powder (5% in the diet) for 21 days on glycolytic, gluconeogenic and NADPlinked lipogenic enzymes were studied in liver and kidney tissues of alloxan-induced diabetic Wistar rats. Diabetic rats were characterised by a 4fold higher blood glucose level and a 0.7fold lower body weight compared to normal controls. The activities of the glycolytic enzymes were significantly lower in the diabetic liver and higher in the diabetic kidney. The activities of gluconeogenic enzymes were higher in both liver and kidney during diabetes, however the activities of the lipogenic enzymes were decreased in both tissues during diabetes. Trigonella seed powder treatment to diabetic rats for 21 days brought down the elevated fasting blood glucose levels to control levels. The altered enzyme activities were significantly restored to control values in both the liver and kidney after Trigonella seed powder treatment. The therapeutic role of Trigonella seed powder in type1 diabetes as exemplified in this study can be attributed to the change of glucose and lipid metabolising enzyme activities to normal values, thus stabilizing glucose homeostasis in the liver and kidney. These biochemical effects exerted by Trigonella seeds make it a possible new therapeutic in type1 diabetes.     

Development of the activities of oxidative, glycolytic and muscle enzymes during early larval life in three families of freshwater fish

The development of the activities of oxidative (COX, CS), glycolytic (PFK, PK, LDH) and muscle enzymes (CK, MK, Pase) was studied in representatives of the families Coregonidae, Salmonidae and Cyprinidae, from hatching to an age of approximately 100 days. In addition, the activities of two enzymes of amino acid metabolism (GOT, GPT) were followed in rainbow trout and in roach.
Water content of fresh body weight and protein content of dry body weight decrease during the early larval period. Specific activities of the two oxidative enzymes decline, whereas those of glycolytic and muscle enzymes increase in all species.
A family-specific event is the enormous increase in glycolytic and muscle enzymes from very low values in the early larva to very high levels in adult Coregonus sp. In rainbow trout, CS activity begins with a low-level period lasting throughout the yolk-sac period, whereas in the other species CS activity is high immediately after hatching.
Acclimation to either 15 or 20° C has no effect on the mass-specific activities of PFK, M K, CK and Pase in roach and chub, but the former three enzymes appear to be strongly dependent on rearing conditions during the early larval period, whereas Pase is not.     

The Development of Enzymes of Energy Metabolism in the Brain of a Precocial (Guinea Pig) and Non-Precocial (Rat) Species

Abstract: Key enzymes of ketone body metabolism (3-hydroxybutyrate de-hydrogenase, 3-oxo-acid: CoA transferase, acetoacetyl-CoA thiolase) and glucose metabolism (hexokinase, lactate dehydrogenase, pyruvate dehydrogenase, citrate synthase) have been measured in the brains of foetal, neonatal and adult guinea pigs and compared to those in the brains of neonatal and adult rats. The activities of the guinea pig brain ketone-body-metabolising enzymes remain relatively low in activity throughout the foetal and neonatal periods, with only slight increases occurring at birth. This contrasts with the rat brain, where three- to fourfold increases in activity occur during the suckling period (0–21 days post partum), followed by a corresponding decrease in the adult. The activities of the hexokinase (mitochondrial and cytosolic), pyruvate dehydrogenase, lactate dehydrogenase and citrate synthase of guinea pig brain show marked increases in the last 10–15 days before birth, so that at birth the guinea pig possesses activities of these enzymes similar to the adult state. This contrasts with the rat brain where these enzymes develop during the late suckling period (10–15 days after birth). The development of the enzymes of aerobic glycolytic metabolism correlate with the onset of neurological competence in the two species, the guinea pig being a "precocial" species born neurologically competent and the rat being a "non-precocial" species born neurologically immature. The results are discussed with respect to the enzymatic activities required for the energy metabolism of a fully developed, neurologically competent mammalian brain and its relative sensitivity to hypoxia.     

Alterations in some membrane properties in rat brain following exposure to lead

The effect of lead exposure on intracellular calcium levels, membrane fluidity, lipid peroxidation, acetylcholinesterase and monoamine oxidase activity and its accumulation in different regions of the brain were studied to understand the molecular mechanism of lead induced neurotoxicity. Lead treatment (20 mg/kg lead nitrate, intraperitoneally, once daily for 15 days) resulted in a significant accumulation of lead in all brain regions with the maximum being in the hippocampus. Levels of glutathione, lipid peroxidation, intracellular calcium and membrane fluidity, as well as the activity of the membrane bound enzymes, acetylcholinesterase and monoamine oxidase, increased to a significant level in certain areas of the rat brain. The results suggest that lead exerts neurotoxic effects by altering certain membrane bound enzymes and may cause oxidative stress.     

Ethylene dibromide: effects of paternal exposure on the neurotransmitter enzymes in the developing brain of F1 progeny

The effects of ethylene dibromide (EDB) exposure to male rats on several neurotransmitter enzymes have been examined in various brain regions of the F1 progeny, from 7 to 90 days of age. The choline acetyltransferase activity was significantly increased at 21 days old, in most brain regions studied in the F1 progeny of the EDB-treated males, but not at 7, 14 or 90 days old. The acetylcholinesterase activity was altered in different brain regions of the F1 progeny of the EDB-exposed males at both 14 and 21 days old but not at 7 or 90 days old. Glutamic acid decarboxylase activity was increased in corpus striatum but decreased in frontal cortex only at 21 days of age. These neurochemical changes in the developing brain of F1 progeny of EDB-treated males at low doses may be associated with behavioral abnormalities observed early in their development.     

Na+,K+-ATPase and Mg2+-ATPase Activities in Different Regions of Rat Brain During Alloxan Diabetes

The effect of alloxan diabetes on the activities of Na+,K+-ATPase and Mg2+-ATPase was studied in three regions of rat brain at various time intervals after the onset of diabetes. It was observed that Na+,K+-ATPase activity increased at early time intervals after diabetes, followed by a recovery to near control levels in all three regions of the brain. There was an overall increase in Mg2+-ATPase activity in all the regions. A reversal of the effect was observed with insulin administration to the diabetic rats.     

Effects of maternal diabetes on the development of carbohydrate metabolizing enzymes in fetal rat liver

Effects of streptozotocin-induced maternal diabetes on fetal hepatic carbohydrate-metabolizing enzyme development and hormonal status has been explored in the rat. Hepatic glycogen synthase a activity of the normal fetus rose to a maximum at 20 days of gestation, then fell prior to parturition. In fetuses of diabetic mothers, this prepartum decline was curtailed, resulting in enhanced synthase a activity and increased glycogen content in fetal livers at term. Elevation in hepatic synthase a in fetuses of diabetic mothers was due, not to altered interconversion between existing synthase a and b, but to equivalent increases in both forms of the enzyme. Both hepatic and free plasma corticosterone levels were elevated in fetuses of diabetic mothers and may be responsible for the enhanced development of total glycogen synthase observed in these fetuses. In normal fetuses hepatic phosphofructokinase and pyruvate kinase activities also rose to maxima at 20 days, then declined prior to term. In fetuses of diabetic mothers pyruvate kinase activity attained higher than normal maximal levels and phosphofructokinase activity fell more gradually, thus resulting in elevations in both enzyme activities at term. Augmentations in these glycolytic enzymes are compatible with hyperinsulinemia observed in fetuses of diabetic mothers. The following conclusions may be drawn from these findings. During late fetal life developmental patterns of rate-limiting hepatic glycogen-synthesizing and glycolytic enzymes are adapted to glucose utilization. In the normal fetus these patterns reverse at term, thereby promoting glucose mobilization, which prepares the fetus for abrupt deprivation of maternal glucose at birth. Maternal diabetes results in retardation of these reversal processes, presumably due to elevations in fetal glucocorticoid and insulin levels. Glycogenolytic and glucogenic capacities are thereby impaired in these fetuses.     

METABOLIC CONTROL MECHANISMS IN MAMMALIAN SYSTEMS

Abstract— The regulation by thyroid hormone of the activities of hexokinase (ATP: D-hexose 6-phosphotransferase; EC 2.7.1.1), phosphofructokinase (ATP: D-fructose-6- phosphate 1-phosphotransferase; EC 2.7.1.11) and pyruvate kinase (ATP: pyruvate phosphotransferase; EC 2.7.1.40) has been investigated in the soluble fractions of the cerebral cortex and cerebellum of the rat. Ontogenetic studies on these key glycolytic enzymes demonstrated marked increases in the normal cerebral cortex between 1 day and 1 yr of age; less pronounced increases in enzyme activities were noted in the normal cerebellum. Neonatal thyroidectomy, induced by treatment of 1-day-old rats with 100 μCi of ¹³¹I, ied to an impairment of body and brain growth and inhibited the developmental increases in hexokinase, phosphofructokinase and pyruvate kinase in both the cerebral cortex and cerebellum. Whereas 50 μCi of ¹³¹I had little or no effect on these brain enzymes, 200 μCi of the radioisotope markedly inhibited (35–65 per cent) the developmental increases of the various enzyme activities investigated. When administration of the radioisotope was delayed for 20 days after birth, little or no inhibition of the development of brain glycolytic enzymes was observed. Whereas treatment of normal neonatal animals with L-tri-iodothyronine had no significant effect on the activities of cerebro-cortical and cerebellar glycolytic enzymes, the hormone increased their activities in young cretinous rats. However, when the initiation of tri-iodothyronine treatment was delayed until neonatally thyroidectomized rats had reached adulthood, this hormone failed to produce any appreciable change in enzyme activity. Our results indicate that thyroid hormone exerts an important regulatory influence on the activities of hexokinase, phosphofructokinase and pyruvate kinase in the developing cerebral cortex and cerebellum.     

Increased glucose metabolism and ATP level in brain tissue of Huntington's disease transgenic mice

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by multifarious dysfunctional alterations including mitochondrial impairment. In the present study, the formation of inclusions caused by the mutation of huntingtin protein and its relationship with changes in energy metabolism and with pathological alterations were investigated both in transgenic and 3-nitropropionic acid-treated mouse models for HD. The HD and normal mice were characterized clinically; the affected brain regions were identified by immunohistochemistry and used for biochemical analysis of the ATP-producing systems in the cytosolic and the mitochondrial compartments. In both HD models, the activities of some glycolytic enzymes were somewhat higher. By contrast, the activity of glyceraldehyde-3-phosphate dehydrogenase was much lower in the affected region of the brain compared to that of the control. Paradoxically, at the system level, glucose conversion into lactate was enhanced in cytosolic extracts from the HD brain tissue, and the level of ATP was higher in the tissue itself. The paradox could be resolved by taking all the observed changes in glycolytic enzymes into account, ensuing an experiment-based detailed mathematical model of the glycolytic pathway. The mathematical modelling using the experimentally determined kinetic parameters of the individual enzymes and the well-established rate equations predicted the measured flux and concentrations in the case of the control. The same mathematical model with the experimentally determined altered V(max) values of the enzymes did account for an increase of glycolytic flux in the HD sample, although the extent of the increase was not predicted quantitatively. This suggested a somewhat altered regulation of this major metabolic pathway in HD tissue. We then used the mathematical model to develop a hypothesis for a new regulatory interaction that might account for the observed changes; in HD, glyceraldehyde-3-phosphate dehydrogenase may be in closer proximity (perhaps because of the binding of glyceraldehyde-3-phosphate dehydrogenase to huntingtin) with aldolase and engage in channelling for glyceraldehyde-3-phosphate. By contrast to most of the speculation in the literature, our results suggest that the neuronal damage in HD tissue may be associated with increased energy metabolism at the tissue level leading to modified levels of various intermediary metabolites with pathological consequences.     

Different activity of glyoxalase system enzymes in specimens of Sparus auratus exposed to sublethal copper concentrations

The present study regards possible changes in the activity of glyoxalase system enzymes (glyoxalase I, GI, and glyoxalase II, GII) in tissues (brain, liver and white muscle) of the mediterranean bony fish Sparus auratus after a 20 days exposure to sublethal concentrations (0.1 or 0.5 ppm) of Cu in the marine water and on control untreated animals. The experiments also included measurements of copper concentration in the tissues, as well as of lactate dehydrogenase (LDH) activity, to evaluate possible Cu accumulation and changes in glycolytic activity respectively. Cu accumulation only occurs in the liver. GI, GII and LDH activities kept unchanged in the brain after copper exposure. GI activity in liver and muscle of copper-exposed animals decreases probably for a slackening in the glycolytic rate, as suggested by the lowering of LDH activity. GII activity remains unchanged or increases (liver extract, 0.5 ppm of Cu), maybe to safeguard enough cellular levels of GSH.     

Effect of thyroid hormones on the glycolytic enzyme activity in brain areas of the rat

The glycolytic metabolism through the key enzymes, hexokinase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase, have been studied in the brain areas: anterior cortex, amygdala, hypothalamus, septum and hippocampus in adult rats with pharmacologically induced hyperthyroidism. The oxidative metabolism of glucose is accelerated in most brain areas by treatment with high doses of T3, as is shown by the increase in HK activity, approaching normality on reducing the dose. This decrease can also by observed in the PFK activity through the effect of assayed doses of thyroxine. The anterior cortex is the only brain area that does not show significant variations of PK activity through the effects of treatment with thyroid hormones. On the other hand, a general inhibition of the glycolytic anaerobic pathway by treatment with T3 was observed.     

Changes in food intake and glucosensing function of hypothalamus and hindbrain in rainbow trout subjected to hyperglycemic or hypoglycemic conditions

To evaluate the possible role of glucose in the control of food intake (FI) in fish and the involvement of glucosensing system in that role, we have subjected rainbow trout (via intraperitoneal injections) to control, hyperglycemic (500 mg kg(-1) glucose body mass) or hypoglycemic (4 mg kg(-1) bovine insulin) conditions for 10 days. The experimental design was appropriate since hypoglycemia and hyperglycemia were observed the first 5 days after treatment and changes observed in metabolic parameters in liver were similar to those of fish literature. Hyperglycemic conditions elicited small changes in FI accompanied by increased glucose and glycogen levels, glucokinase (GK) activity and glycolytic potential in hypothalamus and hindbrain. In contrast, hypoglycemic conditions elicited a marked increase in FI accompanied by decreased glucose and glycogen levels and GK activity in the same brain regions whereas both regions displayed different responses in glycolytic potential. These results allow us to hypothesize that, despite the relative intolerance to glucose of carnivorous fish, changes in plasma glucose levels in rainbow trout detected by glucosensing areas in brain regions (hypothalamus and hindbrain) are integrated in those or near areas eliciting a response in FI, which was more important under hypoglycemic than under hyperglycemic conditions.     

Prior PCB exposure suppresses hypoxia-induced up-regulation of glycolytic enzymes in Fundulus heteroclitus

Increased activity of the glycolytic enzymes is a conserved feature of the cellular response to hypoxia, and may represent a protective mechanism by which cells can survive short-term hypoxic exposure. Gene induction by hypoxia involves a dimer of the hypoxia inducible factor (HIF)-1 alpha and the nuclear cofactor HIF-1 beta, also called the aryl hydrocarbon receptor nuclear translocator (ARNT), which is also involved in induction of genes in response to aryl hydrocarbon exposure. To assess the possibility of interaction between these pathways, we examined changes in the activity of the glycolytic enzymes in response to hypoxia and polychlorinated biphenyl (PCB) exposure in the liver of a teleost fish, Fundulus heteroclitus. After 3 days of hypoxic exposure (dissolved oxygen levels between 1.5 and 2.0 mg/L), there were significant increases in the activity of six glycolytic enzymes (PGI, ALD, TPI, PGK, PGM and LDH). In contrast, intraperitoneal injection of 1 microg/g body weight of PCB #77 (3,3',4,4'-tetrachlorobiphenyl) caused significant decreases in glycolytic enzyme activity after 7 days of exposure. When fish were injected with PCB #77 and then (4 days later) exposed to hypoxia for 3 days as before, we observed no induction of the glycolytic enzymes. This suggests that there is an antagonistic interaction between exposure to PCBs and hypoxia in F. heteroclitus. Prior PCB exposure could make these fish less tolerant of environmental hypoxia.