Dietary regulation of 6-phosphogluconate dehydrogenase synthesis

Gender- and age-related changes in 6-phosphogluconate dehydrogenase gene expression in white adipose tissue of rats (Rattus norvegicus) are not related to serum testosterone concentration

Previously, we have shown that the age-related changes in 6-phosphogluconate dehydrogenase (6PGDH) activity depend on sex, and that oestradiol is playing a crucial role in the regulation of 6PGDH gene expression in rat liver, but not in other tissues [Pankiewicz, A., Sledzinski, T., Nogalska, A., Swierczynski, J., 2003. Tissue specific, sex and age-related differences in the 6-phosphogluconate dehydrogenase gene expression. Int. J. Biochem. Cell Biol. 35, 235-245.]. To complete the knowledge on the influence of sex hormones on 6PGDH activity, experiments have been performed on the effect of testosterone on 6PGDH gene expression in rat white adipose tissue and liver. The results presented here disclosed that in young male rats high serum testosterone concentration was associated with high white adipose tissue 6PGDH activity. After orchidectomy, a decrease in serum testosterone concentration (both in young and old rats) was observed. In contrast, no changes in white adipose tissue and liver 6PGDH activity were found. In female rats, both young and old, serum testosterone concentration was below the limit of detection, whereas 6PGDH activity was much higher in young than in old animals. Moreover, the testosterone administration to 9-month old male rats (which displayed much lower serum testosterone concentration that young animals) resulted in no effect on 6PGDH activity either in WAT or in the liver. In conclusion, the results presented in this paper indicate that testosterone does not play any role in the age- and gender-related differences in 6PGDH gene expression in white adipose tissue.

Transcriptional regulation of mouse 6-phosphogluconate dehydrogenase by ADD1/SREBP1c

6-Phosphogluconate dehydrogenase (6PGDH) constitutes the pentose phosphate pathway and produces NADPH. 6PGDH is also considered as a lipogenic gene since NADPH is a pivotal cofactor for lipogenesis. Thus, it is important to elucidate how 6PGDH is regulated by various signals related to energy homeostasis. Here, we provide several evidences that ADD1/SREBP1c regulates the expression of mouse 6PGDH gene. DNase I footprinting assay and point mutation studies revealed that the E-box (CANNTG) motif in the promoter of mouse 6PGDH is an important cis-regulatory element for ADD1/SREBP1c. 6PGDH mRNA is highly expressed in white adipose tissue and tightly modulated by nutritional status. Furthermore, we found that ADD1/SREBP1c mediates insulin-dependent 6PGDH expression and that PI3-kinase is an important linker for its regulation. Taken together, these data suggest that ADD1/SREBP1c is a key transcription factor for 6PGDH gene expression and would coordinate glucose metabolism and lipogenesis for energy homeostasis.

Tissue specific, sex and age--related differences in the 6-phosphogluconate dehydrogenase gene expression

Data presented in thid paper indicate that: (1) the age-related changes in 6-phosphogluconate dehydrogenase (6PGDH) activity depend on sex and tissue. No differences in the liver 6PGDH activity between young (1-month-old) males and females were found. In adult males, the activity was the same as in young animals but, in adult females, it reached the value twice as high as in the young. In adipose tissue (both white and brown) and kidney cortex, the enzyme activity decreased with age both in males and females. There were no differences between males and females 6PGDH activity in brain, heart and skeletal muscle. (2) The sex and age-related changes in the liver 6PGDH activity occur predominantly at the level of mRNA cellular concentration. (3) In the liver of ovariectomized rats decrease of 6PGDH activity and mRNA level was observed. Oestradiol administration to ovariectomized rats restored liver 6PGDH activity and liver 6PGDH mRNA levels to that observed in controls. No changes in 6PGDH activity and mRNA levels were found in white adipose tissue (WAT) of ovariectomized adult rats and in ovariectomized rats treated with oestradiol. (4) Oestradiol administration to males caused an increase of liver 6PGDH activity and mRNA levels to values observed in females, but was without an effect on WAT 6PGDH activity and mRNA level. (5) These results suggest that 6PGDH activity in different tissues is not regulated in coordinate fashion and that oestradiol plays an important role in the liver enzyme activity regulation.

Kinetic properties of hexose-monophosphate dehydrogenases. II. Isolation and partial purification of 6-phosphogluconate dehydrogenase from rat liver and kidney cortex

6-Phosphogluconate dehydrogenase (6PGDH) from rat-liver and kidney-cortex cytosol has been partially purified and almost completely isolated (more than 95%) from glucose-6-phosphate dehydrogenase activity. The purification and isolation procedures included high-speed centrifugation, 60-75% ammonium-sulphate fractionation, by which both hexose-monophosphate dehydrogenases activities were separated, and finally the protein fraction was applied to a chromatographic column of Sephadex G-25 equilibrated with 10 mM Tris-EDTA-NADP buffer, pH 7.6, to eliminate any contaminating metabolites. The kinetic properties of the isolated partially purified liver and renal 6PGDH were examined. The saturation curves of this enzyme in both rat tissues showed a typical Michaelis-Menten kinetic, with no evidence of co-operativity. The optimum pH for both liver and kidney-cortex 6PGDH was 8.0. The Km values of liver 6PGDH for 6-phosphogluconate (6PG) and for NADP were 157 microM and 258 microM respectively, while the specific activity measured at optimum conditions (pH 8.0 and 37 degrees C) was 424.2 mU/mg of protein. NADPH caused a competitive inhibition against NADP with an inhibition constant (Ki) of 21 microM. The Km values for 6PG and NADP from kidney-cortex 6PGDH were 49 microM and 56 microM respectively. The specific activity at pH 8.0 and 37 degrees C was 120.7 mU/mg of protein. NADPH also competitively inhibited 6PGDH activity, with a Ki of 41 microM. This paper describes a quick, easy and reliable method for the separation of the two dehydrogenases present in the oxidative segment of the pentose-phosphate pathway in animal tissues, eliminating interference in the measurements of their activities.

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)

The inhibitory effect of actinomycin D and cycloheximide on the increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in experimentally induced diseased skeletal muscles

The myotoxic effect of the subcutaneous administration of N,N1-dimethyl-p-phenylenediamine (DPPD) in rats was enhanced by the simultaneous administration of hyaluronidase. The resulting myopathy was associated with an early and dramatic increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Administration of actinomycin D or cycloheximide prior to the combined DPPD and hyaluronidase treatment prevented the increase in activity of both pentose phosphate pathway enzymes, indicating that the increase in activity requires RNA synthesis and protein synthesis. The possibility that the increase in activity of both NADPH-regenerating enzymes results from the modification by effectors of existing less active forms of these enzymes leading to more highly active forms was refuted.

Kinetics for changes in enzyme synthesis and mRNA content and hormones required for induction of 6-phosphogluconate dehydrogenase in hepatocytes

Rats fasted for 2 days were refed a 60% glucose diet for varying periods of time in order to follow the kinetics for changes in 6-phosphogluconate dehydrogenase synthesis and mRNA content. Hepatocytes isolated from control or induced rats were incubated with actinomycin D and the rate of decline in 6-phosphogluconate dehydrogenase mRNA was determined by translating RNA in a nuclease-treated reticulocyte lysate. The half-life for 6-phosphogluconate dehydrogenase mRNA under both of these conditions was about 2 h. Thus, increases in transcription or the processing of nuclear RNA may increase 6-phosphogluconate dehydrogenase mRNA during the dietary induction of this enzyme. Hepatocytes prepared from fasted rats were cultured with 5% serum and various hormones and energy sources. If hepatocytes were isolated from thyroidectomized rats and cultured in serum from a thyroidectomized calf, the 4-fold induction of 6-phosphogluconate dehydrogenase was primarily dependent upon added insulin. In the presence of optimal insulin concentrations (10(-7) M) triiodothyronine slightly stimulated 6-phosphogluconate dehydrogenase induction. The gut hormones somatostatin and secretin had no effect on 6-phosphogluconate dehydrogenase induction in cultured hepatocytes. Hepatocytes cultured in carbohydrate-free medium and 5% serum required added insulin for maximal induction. 8-Br-cGMP did not significantly affect 6-phosphogluconate dehydrogenase induction in hepatocytes either in the presence or absence of added insulin. Dibutyryl cAMP did not alter the time course or extent of 6-phosphogluconate dehydrogenase induction in cultured hepatocytes. We have concluded that under these conditions insulin is a potent signal regulating the levels of 6-phosphogluconate dehydrogenase mRNA and that this induction is not mediated by cyclic nucleotides.

Induction of mitochondrial phosphoenolpyruvate carboxykinase in the liver of Rana catesbeiana tadpole treated with 3,5,3'-triiodothyronine and undergoing natural metamorphosis

The rates of synthesis and degradation of mitochondrial phosphoenolpyruvate carboxykinase (GTP: oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32) in the liver of tadpoles in the two developmental stages (stages VIII and XXII), and in those treated with 3,5,3'-triiodothyronine, were studied by immunochemical techniques. The rate of synthesis of the enzyme was found to be accelerated at 9 h and 6 days after triiodothyronine administration and also during natural metamorphic climax. No difference was observed in the degradation rate of the enzyme between the tadpoles in the two stages, VIII and XXII.

The increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in skeletal muscles of rats after subcutaneous administration of N,N'-dimethyl-para-phenylenediamine

After subcutaneous administration of N,N'-dimethyl-para-phenylenediamine (DPPD) in rats, a myogenic myopathy was produced in the skeletal muscles. In this communication, the results of the application of various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases and biochemical techniques for the estimation of activities of oxidoreductases in the experimental skeletal muscles are presented. The most striking results was the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase which increased dramatically during the early phase of the muscle disease. The increase in activity of the pentose phosphate shunt enzymes was the first pathological alteration and was present as early as 8 h after a single injection of DPPD. Histochemical techniques for demonstration of activity of both enzymes are therefore highly suited for the detection of minor diseases and the early onset of major diseases of the neuromuscular system. Some glycolytic enzymes as well as some enzymes of the aerobic part of the metabolism showed an early decrease or increase in activity indicating a metabolic imbalance in the muscle fibres. There were more fibres with an intermediate pattern of the energy yielding enzymes in the experimental muscle specimens then in specimens from the control groups. The activity of the catabolic hydrolytic enzymes was strongly increased in pathological muscles. The aerobic muscles were more vulnerable to DPPD than the anaerobic muscles.

NADP-dependent dehydrogenases in rat liver parenchyma. III. The description of a liponeogenic area on the basis of histochemically demonstrated enzyme activities and the neutral fat content during fasting and refeeding

The activities of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase(6PGDH), malic enzyme (ME) and isocitrate dehydrogenase (ICDh) were investigated with optimized histochemical methods (Rieder it al 1978), and the activity of 3-hydroxybutyrate dehydrogenase (3HBDH) and neutral fat content with conventional techniques in the liver of male rats under the following experimental dietary conditions: (A) Fasting for 0, 12 and 84h; (B) 84-h fasting followed by refeeding with a low-fat, high-carbohydrate diet for 6 h and for 2, 3, 5, 7, 11 and 14 nights; (C) refeeding with standard diet for 5 nights; (D) low-fat high-carbohydrate diet for 7 an 14 nights. The activities of G6PDH, 6PGDH and ME decreased slightly during fasting primarily in zone 1 and increased dramatically on refeeding with a low-fat, high-carbohydrate diet. This activity increase was confined mainly to zone 3 during the first 3 days and was accompanied by a deposition of neutral fats that began in zone 3 and progressed to zone 1. Neutral for accumulation was maximal after 3 nights, with a uniform accumulation of large droplets in all the hepatocytes; this was followed by a release that started in zone 3 and proceeded in a periportal direction. On the other hand, G6PDH, 6PGDH and ME attained their maximum activities after 5 amd 7 nights of low-fat diet, the activities being nearly homogeneously distributed over the liver acinus in a few cases. Subsequently the activities fill mainly in zone 1, causing the activity patterns and levels to approach those of the animals in group (D). In contrast to this, the activity of ICDH increased during fasting principally in zone 1, so that the otherwise steep activity gradient in favor of zone 3 lessened. Refeeding led at first to a fall of activity below the initial value, but later the normal distribution pattern was restored. The activity of 3HBDH showed a behavior similar to that of ICDH. The findings are discussed with reference to the functional heterogeneity of the liver parenchyma, and the existence of a liponeogenic area in zone 3 is proposed.

A new method for measuring covalent binding of chemicals to cellular macromolecules

A new method has been developed for measuring the total covalent binding of metabolically activated compounds to cellular macromolecules. This method employs equilibrium dialysis, in the presence of the detergent sodium dodecyl sulfate (SDS), to remove unbound radiolabeled compound and its metabolites from cellular macromolecules. [14C] Bromobenzene (80 microM), [14C]aflatoxin B1 (5 microM) or 3-[14C]methylcholanthrene (100 microM) was incubated (37 degrees C) with primary hepatocytes or liver microsomes isolated from Fischer-344 rats. The covalent binding of 14C-radiolabel to hepatic or microsomal macromolecules was measured by SDS-equilibrium dialysis and compared with that measured by exhaustive extraction. After 1 h of incubation with hepatocytes or microsomes, 2--7 times more covalent binding was detected by SDS-equilibrium dialysis, than by exhaustive extraction. The radioactivity associated with these hepatic or microsomal macromolecules migrated to discrete positions on SDS-polyacrylamide disc gels. The non-dialysable radioactivity from incubations with [14C] bromobenzene could not be extracted with diethyl ether even after treatment of the dialysin with beta-glucuronidase-sulfatase or dilute acid. This was taken to indicate that the radioactivity in the dialysin did not include free bromobenzene or its metabolites, a conclusion supported by thin-layer chromatography analysis of the dialysin. The lower amount of covalent binding detected by exhaustive extraction may be related to the inability of trichloroacetic acid to quantitatively precipitate small molecular weight macromolecules. SDS-equilibrium dialysis is an easy, rapid and non-destructive technique for measuring covalent binding. The macromolecular integrity of the sample is maintained and allows further studies concerning the specificity of the covalent interactions.