Hexose Monophosphate Shunt Dehydrogenases Research Articles

Unusual increase of lipogenesis in rat white adipose tissue after multiple cycles of starvation-refeeding

The purpose of the study was to determine the response of liver and brown (BAT) and white (WAT) adipose tissue lipogenesis and total body weight in rats subjected to multiple cycles of 3 days of fasting and 3 days of refeeding. Rats fasted for 3 days showed significant reduction in body weight. These changes were reversed on 3 days' refeeding. Body weight was much higher in rats fed ad libitum than in animals experiencing more than one cycle of 3 days of fasting followed by 3 days of refeeding. Despite the significant body weight reduction, an unusual increase of lipogenesis in WAT was found after multiple cycles of starvation-refeeding of rats on standard laboratory diet. The rate of lipogenesis in the liver and BAT was also elevated but to a much smaller extent. A parallel increase in enzymatic activities related to fatty acid synthesis, ie, fatty acid synthase, acetyl-coenzyme A carboxylase, adenosine triphosphate (ATP)-citrate lyase, NADP-linked malic enzyme, and hexose monophosphate shunt dehydrogenases, suggests that the increased rate of lipogenesis in WAT is a consequence of increased lipogenic enzyme activities. These data suggest that upregulation of WAT lipogenesis occurs after the multiple cycles of the starvation-refeeding protocol. An unusual increase of lipogenesis in rat WAT may have a survival advantage, because starved-refed rats must develop the ability to ingest large amounts of food during a refeeding period to store it in a convenient form than can be used as an oxidizable substrate during a period of starvation. Moreover, these results suggest that it is possible to develop appropriate starvation-refeeding conditions that may inhibit body weight gain.

Glucose-6-phosphate dehydrogenase deficiency severely restricts the biotransformation of daunorubicin in human erythrocytes

Recognition and analysis of distinct mechanisms by which primaquine and other hemolytic drugs activate the hexose monophosphate shunt (HMS) have suggested a hitherto unsuspected pharmacogenetic interaction between daunorubicin metabolism and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Because this deficiency is very common, and because anthracyclines are indispensable antitumor antibiotics that are biotransformed mainly by carbonyl reductase, we have compared the reductase-mediated conversion of daunorubicin to daunorubicinol and the conversion of doxorubicin to doxorubicinol in G6PD-deficient and nondeficient erythrocytes. We found that even without G6PD deficiency, the HMS dehydrogenases selectively limited daunorubicin metabolism, as contrasted with that of doxorubicin. The milder GdA − variety of G6PD deficiency restricted the biotransformation of daunorubicin at therapeutic levels, in hemolysates and intact erythrocytes, within 15 minutes, for at least 24 hours. The bioconversion defect was even more severe in Gd Mediterranean G6PD deficiency. Primaquine aldehyde competed with daunorubicin as a substrate for carbonyl reductase. These studies show that HMS dehydrogenase activity controls carbonyl reductase-dependent biotransformation. New issues arise concerning possible effects of G6PD deficiency on the oncolytic and toxic properties of anthracyclines that are effective substrates for carbonyl reductase and also on nonxenobiotic reactions catalyzed by this enzyme.

Comparative studies on NADP +-linked malic enzyme in the central nervous system of ectothermic and endothermic animals

The maximum activity and intracellular distribution of NADP +-linked malic enzyme in brain of Mammalia, Aves, Reptilia, Amphibia and Pisces are reported. Malic enzyme activity was present in all animal brains investigated. Most of the enzyme activity was located in the mitochondrial fraction. In brain of endothermic animals the activity of malic enzyme was several-fold higher than in ectothermic animals. Other NADPH-producing enzymes (i.e. NADP +-linked isocitrate dehydrogenase and hexosemonophosphate shunt dehydrogenase) activities were essentially similar in all animal brains tested. However, the total potential capability of NADPH production was lower in ectothermic animals (due mainly to lower malic enzyme activity). It is suggested that the presence of NADP +-linked malic enzyme in the brain may be related mainly to mitochondrial metabolism, especially to maintain the mitochondrial pool of NADP + in reduced form.

Long‐term adaptive response to dietary protein of hexose monophosphate shunt dehydrogenases in rat kidney tubules

We have studied the effects of several different macronutrients on the kinetic behaviour of rat renal glucose 6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Rats were meal-fed with high-carbohydrate/low-protein, high-protein/low-carbohydrate and high-fat diets. High-protein increased renal G6PDH and 6PDGH activities by 66 per cent and 70 per cent respectively, without significantly changing the Km values of either and each Hexose monophosphate dehydrogenase activity increased steadily, reaching a significant difference on day 4. A rise in carbohydrate or fat in the diets, produced no significant change in either the activity or the kinetic parameters, Vmax and Km of the two dehydrogenases. In addition, the administration of a high-protein diet for 8 days significantly increased both the pentose phosphate pathway flux (92.6 per cent) and the kidney weigth (35 per cent), whereas no significant changes in these parameters were found when the animals were treated with the other diets. Our results suggest that an increase in the levels of dietary protein induces a rise in the intracellular levels of these enzymes. The possible role of this metabolic pathway in the kidneys under these nutritional conditions is also discussed.

Comparative studies on lipogenic enzyme activities in the liver of human and some animal species

1. 1. The activities of enzymes involved in fatty acid synthesis in the human liver (sample taken during abdominal surgery) and in the livers of some animals were studied. 2. 2. Fatty acid synthase, ATP-citrate lyase and malic enzyme activities were found to be from 4 to 70-fold lower in human liver than in rat or bird livers. 3. 3. The activities of hexose monophosphate shunt dehydrogenases in human liver were from half to almost equal to the corresponding activities in birds, but much lower than in rat liver. 4. 4. The activities of all enzymes listed above in human and beef liver were very similar (except fatty acid synthase which was undetectable in the beef liver). 5. 5. Very high activity of NADP-linked isocitrate dehydrogenase was found in livers of all species tested. 6. 6. These results are discussed in relation to the role of the human liver in lipogenesis. 7. 7. The activities of the enzymes generating NADPH in human liver taken during abdominal surgery were similar to the activities observed in the tissue obtained post mortem. 8. 8. This suggested that post mortem tissue may be used as a reliable human material for some enzyme assays. 9. 9. Thus we also examined the activity of malic enzyme in post mortem human kidney cortex, heart, skeletal muscle and brain. 10. 10. Relatively high activity of NADP-linked malic enzyme has been observed in human brain.

Influence of experimental diabetes on the kinetic behaviour of renal cortex hexose monophosphate dehydrogenases

1. 1. Short term (1–2 hr) and long-term (2 days) effects of experimental alloxan induced diabetes on the kinetics of the renal hexose monophosphate shunt dehydrogenases are reported. 2. 2. Alloxan diabetes for 2 days significantly increased kidney weight (16%) adding about 80mg/day per g of kidney. No significant changes were found in renal growth 1–2 hr after alloxan injection. 3. 3. Under these experimental conditions, the activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase significantly increased (103 and 33% respectively) at all substrate concentrations, without affecting the K m s of either enzyme. 4. 4. There was no effect of alloxan on the activity of these enzymes at 1–2 hr. Saturation curves show that all enzymes exhibited a M-M kinetic without evidence of sigmoidicity. 5. 5. The results suggest that increased renal hexose monophosphate dehydrogenases activities are due to increased concentrations of the rate limiting proteins. 6. 6. The relationship between these changes and renal hypertrophy is also discussed.

Metabolic characterization of mouse bone marrow cells responsive to estrogenic inhibition: hexose monophosphate shunt enzyme activity in enriched populations of mature cells and progenitor cells.

Compounds with estrogenic activity cause initial toxic responses in the bone marrow characterized by hypocellularity and stem cell myelotoxicity. To elucidate the biochemical nature of these toxic responses, bone marrow cells were collected from mice treated with pharmacological doses of estrogenic chemicals, separated into enriched cell populations, and the enzymatic responses of the individual cell types characterized. Female B6C3F1 mice were injected s.c. with five daily doses of 0.07-5.6 mu moles diethylstilbestrol (DES) or 17-beta estradiol. At 4 days posttreatment body and organ weights were recorded and bone marrow was collected for enumeration and assay of stem cell proliferative responses and enzyme analyses. Treatment with higher dose levels of either estrogenic chemical caused equivalent thymic atrophy, but DES resulted in greater liver and spleen hypertrophy than estradiol. Hexose monophosphate shunt dehydrogenase enzymes in unfractionated bone marrow cells were more sensitive to inhibition by lower estrogen doses than representative enzymes from glycolysis of the Kreb's Cycle, and on an equimolar basis were inhibited to a greater extent by DES than by estradiol. Enzyme analyses after density gradient cell separation indicated that 70-80% of the hexose monophosphate shunt enzyme activity in bone marrow from untreated mice occurred in the enriched band of cells containing predominantly granulocyte-macrophages. The majority of the enzyme inhibition induced by DES treatment could also be ascribed to this cellular population. Furthermore, it was shown that DES had a greater inhibitory effect on the proliferative capacity of the committed stem cells than on the multipotential stem cell population, and the main response was again expressed in the enriched band of cells containing predominantly granulocyte-macrophage precursors. Preliminary endocrine ablation experiments indicated estrogen inhibition of hexose monophosphate shunt enzyme activity was independent of the adrenal and the ovary, but was mediated through the thymus at lower estrogen concentrations.

The influence of prolonged clofibrate treatment on the plasma drug concentration and liver NADP-linked enzymes activity

1. 1. The clofibric acid (CPIB) concentration in the rat blood plasma during 14 days of treatment with clofibrate and after cessation of the treatment, was measured and compared with the changes of some NADP-linked dehydrogenases activity. 2. 2. CPIB rapidly accumulates in the plasma during the first two days of clofibrate administration reaching a maximum concentration of about 0.6 mM. Then a linear decrease of the drug concentration was observed. 3. 3. The second day after clofibrate treatment had been completed, CPIB could no longer be detected in the plasma. 4. 4. Liver malic enzyme activity increased constantly up to the third day after cessation of the treatment. 5. 5. There was a decrease of activity which reached its control level on the 32nd day of the experiment. 6. 6. The variation patterns of hexose monophosphate shunt dehydrogenases activity and liver weight were similar to the changes of malic enzyme activity.

Changes of the NADP-linked malic enzyme in the developing rat skeletal muscle

1. 1. The activities of NADP-linked malic enzyme, hexose monophosphate shunt dehydrogenases and NADP-linked isocitrate dehydrogenase were studied during development of skeletal muscle and compared with those in the liver. 2. 2. The variation patterns of malic enzyme activity in the liver and in the skeletal muscle were very similar, however the amplitude of the changes was different. 3. 3. The enzyme activity increased approx 16-fold in the liver and about 2-fold in skeletal muscle at the same stage of development. 4. 4. In skeletal muscle the increase of the malic enzyme activity was only slightly higher than of lactic dehydrogenase and citrate synthase. 5. 5. Studies on the intracellular distribution of malic enzyme in skeletal muscle showed that both mitochondrial and extramitochondrial enzymes increased between 20th and 37th day of life, the increase of the extramitochondrial enzyme being more pronounced. 6. 6. The hexose monophosphate shunt dehydrogenases activity showed an increase in the liver but no change was observed in the skeletal muscle at the weaning time. 7. 7. Changes in the activity of the liver and skeletal muscle isocitrate dehydrogenase were not significant between 10th and 80th day of life. 8. 8. The results suggest that the malic enzyme in the liver is playing a different physiological role than in the skeletal muscle.

The effect of clofibrate feeding on the NADP-linked dehydrogenases activity in rat tissue

1. Administration of clofibrate to the rat increased several fold the activity of malic enzyme in the liver. Clofibrate treatment resulted also in an increased activity of the hepatic hexose monophosphate shunt dehydrogenases but was without effect on NADP-linked isocitrate dehydrogenase. 2. The increased activity of malic enzyme in the liver resulting from the administration of clofibrate was inhibited by ethionine and puromycin, which suggests that de novo synthesis of the enzyme protein did occur as the result of the drug action. 3. In contrast to the liver malic enzyme, the enzyme activity in kidney cortex increased only two-fold, whereas in the heart and skeletal muscle the activity was not affected by clofibrate administration.

Inhibition of the Induction of Liver Hexose-Monophosphate Shunt Dehydrogenases in the Starved-Refed Rat by Injection of Triton WR-1339

The effect of Triton WR-1339 on induction of liver glucose6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) was investigated. Male rats of the Holtzman strain were starved for 3 days and refed a diet high in carbohydrate (68.9% as glucose monohydrate ). Twenty-four hours prior to refeeding, the experimental rats were injected with 85 mg/100 g body weight of Triton WR-1339 and the control rats were given equal volumes of a physiological saline solution. The induction of the two lipogenesis associated dehydrogenases, G6PDH and 6PGDH, in the liver of the Triton-treated rats, was both delayed and de pressed. Very high triglycA©ridelevels and relatively high hexosaminidase levels were observed in the plasma of the Triton-injected rats, compared with that of plasma of the control rats for most of the experimental period. Three hours after refeeding the diet, a significant elevation in the plasma glucose level was observed in the saline-treated rats but not in the plasma of Triton-intoxicated rats. No significant recompartmentation of lysosomal enzyme activity to liver nuclei occurred as a result of refeeding a carbo hydrate-rich diet when Triton WR-1339 was injected 20 hours before refeed ing. This contrasts with the rapid association of lysosomal enzymes with nuclei from livers of starved rats refed a carbohydrate containing diet, but not treated with the detergent as previously reported from this laboratory. In the present study, the fragility of liver lysosomes of Triton injected, starved rats to homogenization did not change significantly after refeeding a high carbohydrate diet. Thus, Triton inhibited the transient lysosomal fragility previously observed in rats similarly examined, but not injected with Triton WR-1339. J. Nutr. 108: 1566-1571, 1978. INDEXING

Lipogenesis in isolated intramuscular adipose tissue from four bovine muscles.

The incorporation of acetate-l-14C into CO2 and total fatty acids and the activities of NADP-malate dehydrogenase, NADP-isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and acetyl CoA carboxylase were studied in intramuscular adipose tissue from the trapezius, longissimus, semimembranosus and pectoralis profundus muscles of 470 kg, 14-month-old Hereford × Angus steers. It was concluded that intramuscular lipid can be synthesized in situ, but at a slower rate than subcutaneous lipid. The rate of synthesis of fatty acids and CO2 from acetate-l-14C was directly related to adipose cell volume and for this reason the intramuscular adipose tissue of the pectoralis profundus muscle was more active than that of the other three muscles. The activities of the four NADPH-generating enzymes were positively related to both adipose cell volume and fatty acid synthesis. NADP-malate dehydrogenase activity was low in intramuscular adipose tissue; however, the hexose monophosphate shunt dehydrogenases and possibly NADP-isocitrate dehydrogenase are capable of supplying NADPH for fatty acid synthesis in bovine intramuscular adipose tissue.

Growth and intermediary metabolism of larval and metamorphosing stages of the landlocked sea lamprey, Petromyzon marinus L

Seasonal changes in blood, liver and muscle substrate (glucose, glycogen and lipid) concentrations and enzyme (pyruvate kinase (PyK), fructose diphosphatase (FDPase), NADP-isocitrate dehydrogenase (ICDH), malic enzyme (ME) and the hexose monophosphate shunt dehydrogenases (HMSD)) activities were assessed in ammocoete and metamorphosing stages of a stream stock of the landlocked sea lamprey, Petromyzon marinus L. In all developmental stages studied, muscle rather than liver tissue served as the main site of carbohydrate and fat storage. Blood glucose and muscle lipid exhibited a positive relationship while liver HMSD and muscle ME activity, a negative relationship, with ammocoete weight. These responses were attributed to a proliferation of red fibers and adipocytes in the ammocoete muscle as the time of metamorphosis approched. Muscle lipid stores of ammocoetes in their last year of larval life increased dramatically during the fall and winter preceding metamorphosis. Changes in tissue enzyme activity of ammocoetes in their last year of larval life indicated that the liver was the site of amino acid incorporation into fat while muscle was the site of lipogenesis from glucose. During the non-trophic period of metamorphosis, stored material was catabolized to provide energy for protein synthesis.

Energy Metabolism of Brain in Human Protein-Calorie Malnutrition

Cerebral blood flow (CBF) and carbohydrate metabolism were studied in 5 normal children and 25 children, aged 40 months or less, with varying degrees of protein-calorie malnutrition (PCM). CBF in normal children and those suffering from grade I PCM was 90.3 +/- 5.7 ml/100 g/min, a value comparable with that obtained by other investigators, but the proportion of glucose taken up by the brain which combined with oxygen, the oxygen/glucose index (OGI), was 65.8%, indicating significant conversion of glucose into lactic acid. Cerebral lactic acid production was 45.3 micronM/100 g/min, and the respiratory quotient (R.Q.) was 1.00. With increasing severity of PCM, there was increased glucose utilization and a progressive reduction in the OGI. In grade IV PCM, CBF was 68.7 +/- 5.4ml/100g/min, and the OGI was 34.7%. Cerebral lactic acid production was 27.4 micronM/100 g/min, and the R.Q. rose to 1.52. These findings suggest that in severe human PCM the proportion of glucose undergoing aerobic oxidation is reduced, and that in addition to being converted to lactic acid, a significant proportion of glucose is transformed by the brain into long chain fatty acids.

Hexose monophosphate shunt dehydrogenases in the sea urchin and the frog: Comparison of some functional properties of the enzymes in vitro

1. 1. Glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6-PGD) from unfertilized eggs of the sea urchin Arbacia punctulata and from liver and other tissues of the frog Rana pipiens have been partially purified and characterized. 2. 2. Sea urchin egg G6PD has a pH optimum of 8.8–9.2, while frog liver G6PD has optimum activity between pH 7.9 and 8.9; 6-PGD from both sources shows optimum activity between pH 7.9 and 8.6. 3. 3. G6PD from both sources is active with glucose-6-P and galactose-6-P as substrates. Sea urchin egg G6PD also accepts 2-deoxyglucose-6-P as a substrate. 4. 4. Apparent K m's for glucose-6-P are about 4 × 10 −5 M and 4 × 10 −4 M, for sea urchin egg and frog liver G6PD, respectively. 5. 5. High concentrations of ATP and ribose-5-P inhibit G6PD from both sources.

Alterations in the developmental patterns of enzymes in chicken embryos infected with west nile virus

Infection of chicken embryos with West Nile (WN) virus, a group B togavirus containing structural lipids, caused a rapidly developing hypertriglyceridemia. Changes in the activity of several hepatic regulatory enzymes in glycolytic and lipogenic pathways occurred during infection. Compared to control values in embryos of the same age (16 days), an 8.8-fold increase in the specific activity of ATP-citrate lyase and a 5.6-fold increase in that of hexokinase were observed on the third day of WN virus infection. Hexose monophosphate shunt dehydrogenase specific activities were elevated twofold in virus-infected livers. Activities of malic enzyme and phosphofructokinase were also elevated in WN virus-infected livers. Malate dehydrogenase and NADP-linked isocitrate dehydrogenase levels showed little or no change during infection. The levels of pyruvate kinase and lactate dehydrogenase were decreased in virus-infected livers. Hepatic acetyl-CoA carboxylase activity was at least twofold higher in virus-infected embryos; however, following removal of low-molecular-weight compounds, the specific activities of this enzyme from infected and control embryos were virtually identical. The results of mixing experiments suggest that the low levels of carboxylase activity in control embryos may be due to the presence of enzyme inhibitor(s) which can be removed by gel filtration. The incorporation of radiolabeled precursors into cellular lipids by liver minces from virus-infected and uninfected embryos was measured. There was a twofold increase in carbohydrate incorporation in virus-infected liver as compared to uninfected liver; [ 14C]pyruvic acid was incorporated into lipids to the greatest extent. [1- 14C]acetic acid, [U- 14C]alanine, and [U- 14C]leucine were incorporated very poorly in both infected and control livers. Twice as much [1- 14C]oleic acid or [1- 14C oleic]triolein was incorporated in WN-infected livers as in control. The relative distribution of neutral and polar lipids formed from each precursor was generally similar in infected and uninfected livers as determined by thin-layer chromatography of radiolabeled lipids. Except for a threefold increase in oxidation of [ 14C]glucose by virus-infected livers, the oxidations of carbohydrates and fatty acids were similar in infected and uninfected livers. The pentose phosphate pathway appears to be the major pathway utilized in glucose oxidation for both control and virus-infected livers. The results indicate that enhanced flux of metabolites into lipids reflects a virus-induced alteration in embryonic development: The enzyme patterns of infected embryos are more characteristic of older embryos or even newly hatched chicks.

Action of chlorpromazine on spore-forming Bacillus species.

The hypothesis that chlorpromazine inhibition of bacterial endospore germination acts at the level of hexose monophosphate shunt (HMP) dehydrogenases was tested and substantiated for Bacillus cereus T and Bacillus megaterium. However, this cannot be an exclusive mechanism of action in bacterial systems because inhibitory effects on growth and respiration are caused by the drug even when these HMP enzymes are not present in the organisms.

Enzyme activities in skeletal muscle after contractile activity in vitro

1. 1. Changes in muscle enzyme activities following isometric and isotonic contractile activity of electrically stimulated plantaris longus from frog were studied in vitro. The effect of contractile activity under hypoxic conditions and the time-course of changes in enzyme activities after exercise were also investigated. 2. 2. Isometric contractile work caused decreased activities in creatine phosphokinase, phosphorylase and phosphofructokinase and increased activities in hexokinase and cytochrome oxidase. The activity levels of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, pyruvate kinase, lactate dehydrogenase and fumarase were not significantly different from control values. 3. 3. After isotonic contraction no significant changes in creatine phosphokinase, phosphorylase and phosphofructokinase activities were seen. Besides hexokinase and cytochrome oxidase, fumarase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate deh ydrogenase activities were also increased. 4. 4. There were no significant differences between the enzyme response obtained after isometric contractions in deoxygenated or oxygenated medium. 5. 5. After a recovery period for 5 hours following isometric work the activities of hexokinase, the hexose monophosphate shunt dehydrogenases, fumarase and cytochrome oxidase showed increased activities. These declined to control values after 20 hours recovery except for hexokinase and 6-phosphogluconate dehydrogenase. The activity levels of creatine phosphokinase, phosphorylase and phosphofructokinase were progressively decreased during the recovery period. Pyruvate kinase and lactate dehydrogenase also showed decreased activity values after 20 hours recovery.

Enzyme activities in muscle and liver after destruction of the ventromedial hypothalamic area and administration of insulin.

The activities of various enzymes and the glycogen content of skeletal muscle and liver were investigated in rats with hyperinsulinemia, induced by either ventromedial hypothalamic (VMH) lesion or administration of insulin. Three days after hypothalamic surgery the activities of hexokinase and lactate dehydrogenase were increased in muscle tissue. Three months postoperatively the hexokinase activity in muscle was normalized, while those of lactate dehydrogenase and glycerophosphate dehydrogenase were decreased. Daily administration of insulin for two months caused increasing activities of hexokinase, phosphofructokinase and lactate dehydrogenase in muscle. The glycogen content of the muscle was unchanged three days after the VMH lesion as well as after insulin administration. Three months post-operatively the muscle glycogen content was decreased. Qualitatively similar changes with lowered glycogen content and increased activities of glycolytic as well as hexose monophosphate shunt dehydrogenases were obtained in liver 3 months after VMH lesion as well as insulin administration. The results presented do not reveal any peripheral block in the glucose metabolism. This suggests no primary role of muscle tissue in the development of hyperinsulinemia.

Hexose monophosphate shunt dehydrogenases in the developing frog

1. 1. Total activities and specific activities of glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6-PGD) were measured at various stages in the early development of the frog Rana pipiens, and in individual tissues of tadpoles and adult frogs. 2. 2. Total activities and specific activities of both enzymes were low in frog eggs and embryos, but increased markedly during larval development. The ratio of G6PD/6-PGD activities also increased from 1·0 to 3·5 during larval development. 3. 3. Differences were also found in the specific activities and the ratio of the two activities among individual tadpole tissues and between tissues of the tadpoles and adult frogs.