Effects of kainate on glucose metabolising enzymes in the brain

Hexokinase and glucose-6-phosphate dehydrogenase activities were studied in brain regions after intraventricular injection of kainic acid. Hexokinase activity was decreased by 10-15% in various regions while glucose-6-phosphate dehydrogenase activity remained unaltered. Soluble hexokinase activity, which remained the smaller fraction of total hexokinase activity, showed slightly more dramatic decreases of 15-35% compared to normal activities in brain regions. This decrease of hexokinase activity in the cytosolic compartment could partly account for the kainate-induced decreases seen in glucose metabolism.     

Microphotometric determination of enzymes in brain sections

Summary An incubation medium was established for the microphotometric demonstration of glutamate dehydrogenase (Gldh) in cryostat sections of the rat hippocampus which served as an exemplary brain region. The final incubation medium consisted of 100 mM l-glutamic acid monosodium salt, 5 mM NAD, 10 mM sodium azide (NaN₃), 5 mM ADP, 20 mM sodium chloride, 0.15 mM phenazine methosulfate (PMS), 5 mM nitroblue tetrazolium chloride and 22% polyvinyl alcohol (PVA) in 0.05 M Hepes buffer; the final pH was 7.5. — The study showed that in the histochemical demonstration of Gldh the use of relatively high PVA concentrations were necessary to avoid diffusion artefacts because Gldh seems to be only loosely bound to the mitochondrial matrix. The use of NaN₃ as a blocker of the respiratory chain was indispensible, because without NaN₃ most reduction equivalents were lost through the respiratory chain. With PMS as an exogenous electron carrier, the demonstrable Gldh activities increased significantly indicating that, in the case of Gldh, the endogenous NADH tetrazolium reductase was not sufficiently effective. Furthermore, it was shown that Gldh was affected by many small molecules (e.g. activation by sodium ions, inhibition by magnesium and calcium ions) so that minor variations of the incubation conditions may cause major differences in demonstrable activities. Supported by the Deutsche Forschungsgemeinschaft (Ku 541/2-2)     

Microphotometric determination of enzymes in brain sections

Summary An incubation medium was adapted for the microphotometric determination (kinetic and end-point measurements) of the activities of mitochondrial alpha-glycerophosphate dehydrogenase (GPDH) in the rat hippocampus. For comparison, the activities of the cytoplasmic NAD-linked alpha-glycerophosphate dehydrogenase were also measured. The study showed that in the demonstration of both enzymes the use of an exogenous electron carrier is necessary. Both enzymes react to phenazine methosulfate (PMS) which transfers reduction equivalents to the electron acceptor nitroblue tetrazolium chloride (NBT), thus causing a coreaction of GPDH in the demonstration of NAD-GPDH. Therefore, only the NAD-independent GPDH which is stimulated by menadione, can be selectively demonstrated in the histochemical procedure applied. The final incubation medium of GPDH consisted of 15 mMl-glycerol 3-phosphate, 5 mM NBT, 0.4 mM menadione, 7.5% polyvinyl alcohol in 0.05 M Hepes buffer, pH 8; the final pH of the incubation medium was 7.5. A linear response of the reaction lasted about 5 min. There was a linear relationship between section thickness and the formation of reaction product up to a section thickness of 14 microns. The apparent K_m value at 25°C was 0.6 mM. It is concluded that using menadione histochemical methods are suited to determine the mitochondrial GPDH activities in brain sections whereas using PMS a coreaction of GPDH takes place in the demonstration of NAD-GPDH, so that a histochemical quantification of NAD-GPDH cannot be recommended.     

Microphotometric determination of enzymes in brain sections

Summary A histochemical procedure was established for the microphotometric determination of hexokinase (HK) in sections of the rat hippocampus, which served as an exemplary brain region. For this quantitative procedure, slides were coated with glucose 6-phosphate dehydrogenase (G6PDH) as an auxiliary enzyme and sections were mounted onto this enzyme film. The sections were then incubated with the following adapted incubation medium: 5 mM d-glucose, 1.5 mM NADP, 7.5 mM ATP, 4 mM nitroblue tetrazolium chloride, 10 mM NaN₃, 10 mM MgCl₂, 0.25 mM phenazine methosulfate, 1 U/ml G6PDH, 22% polyvinyl alcohol in 0.05 M Hepes buffer; the final pH was 7.5. A linear response of the reaction was observed in the initial 10 min of reaction (kinetic and end-point measurements). The relationship between HK activity and section thickness was linear up to 5 m. The need for such thin sections is discussed in relation to the limited penetration of the auxiliary enzyme into the section. It is concluded that the quantitative demonstration of HK in brain sections could be a valuable tool for studying the local metabolic entrance of glucose in the glycolytic pathway.Supported by the Deutsche Forschungsgemeinschaft (Ku 541/2-1, 2-2)     

Steroid sulfatase and sulfuryl transferase activity in monkey brain tissue

Dehydroepiandrosterone and its sulfated form are commonly known as modulators of gamma-aminobutyrate A and N-methyl-D-aspartate receptors. In spite of poor permeability of the blood-brain barrier for sulfated steroids, high concentrations of dehydroepiandrosterone and also its sulfate have been found in brain tissue. Physiological concentrations of these neuromodulators are maintained by two enzymes present in the blood and many peripheral tissues, including the brain, namely, steroid sulfatase and neurosteroid sulfuryl transferase (NSST). This prompted us to investigate activities of these enzymes in primate brain tissue. Rather low neurosteroid sulfuryl transferase activity was detectable in in vitro incubations of cytosol fractions from male and female Macaca mulatta brains, dissected to cerebral cortex, subcortex, and cerebellum. In male monkeys, the highest activity was found in the cerebellum followed by cortex and subcortex. On the other hand, in female monkeys, the highest activity was determined in the cortex followed by subcortex and cerebellum. Steroid sulfatase activity was determined in in vitro microsomal samples from each of the above-mentioned brain regions. Specific activities in female cerebral regions declined in the order: cerebellum, cortex, and subcortex. In male monkeys, no significant difference among the studied regions was observed. Using dehydroepiandrosterone sulfate as a substrate, the apparent kinetic characteristics of steroid sulfatase were determined as follows: K(M) 36.10 +/- 8.33 microM, V(max) 8.38 +/- 1.68 nmol/h/mg protein. These results will serve as a basis for further studies concerning the pathophysiology of human brain tumors.     

Extraction and study of soil enzymes metabolising tryptophan

Summary The dialysed humic acids obtained from a forest Mull by extraction of a diluted solution of sodium carbonate are enzymatically active. It is found by radiorespirometry that the humic acids act on thel-tryptophan carboxyl C¹⁴, although thed-tryptophan carboxyl suffers no attack. The methylene group and the indole and benzene nuclei are not broken down. Only the carboxyl function is mineralised. Radiochromatography shows that through the action of the humic acids the tryptophan is broken down primarily into indoleacetamide and secondarily into β-indoleacetic acid. From the nature of these compounds it is assumed that the humic acids have an oxygenas effect on thel-tryptophan. The enzymatic activity has its optimum value at 65°C. It is partially inhibited by lyophilisation and by toluene. The pyridoxal phosphate (0.1 μM) has a slight activating influence. The alkalis and mineral acids decompose the enzyme. We can therefore see just how much importance attaches to the humic matter, not only as an energy substrate reserve for the micro-organisms and plants but also as a site for biological activities which are quite distinct from any microbial proliferation and the role of which in plants has still to be studied. It would be of interest to determine the presence of this enzymatic system in other pedologically defined soils and to study it in correlation with their fertility. In addition, there remains the task of detecting the microbial agents in the soil which contribute to the formation of this remarkable enzymatic system.     

Cell cycle effect on the activity of deoxynucleoside analogue metabolising enzymes

Deoxynucleoside analogues (dNAs) are cytotoxic towards both replicating and indolent malignancies. The impact of fluctuations in the metabolism of dNAs in relation to cell cycle could have strong implications regarding the activity of dNAs. Deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK) are important enzymes for phosphorylation/activation of dNAs. These drugs can be dephosphorylated/deactivated by 5'-nucleotidases (5'-NTs) and elevated activities of 5'-NTs and decreased dCK and/or dGK activities represent resistance mechanisms towards dNAs. The activities of dCK, dGK, and three 5'-NTs were investigated in four human leukemic cell lines in relationship to cell cycle progression and cytotoxicity of dNAs. Synchronization of cell cultures to arrest in G0/G1 by serum-deprivation was performed followed by serum-supplementation for cell cycle progression. The activities of dCK and dGK increased up to 3-fold in CEM, HL60, and MOLT-4 cells as they started to proliferate, while the activity of cytosolic nucleotidase I was reduced in proliferating cells. CEM, HL60, and MOLT-4 cells were also more sensitive to cladribine, cytarabine, 9-beta-D-arabinofuranosylguanine and clofarabine than K562 cells which demonstrated lower levels and less alteration of these enzymes and were least susceptible to the cytotoxic effects of most dNAs. The results suggest that, in the cell lines studied, the proliferation process is associated with a general shift in the direction of activation of dNAs by inducing activities of dCK/dGK and reducing the activity of cN-I which is favourable for the cytotoxic effects of cladribine, cytarabine and, 9-beta-D-arabinofuranosylguanine. These results emphasize the importance of cellular proliferation and dNA metabolism by both phosphorylation and dephosphorylation for susceptibility to dNAs. It underscores the need to understand the mechanisms of action and resistance to dNAs in order to increase efficacy of dNAs treatment by new rational.     

Perturbation of rat hepatic metabolising enzymes by folic acid supplementation

An adequate folate intake minimizes the risk of various cancers and other disorders such as vascular diseases and neural tube defects. However, meta-analyses revealed difficulties in supporting the relationship between folate intake and the risk of cancer. Interestingly, there have been no reports to date on the potential ability of folate to modulate xenobiotic metabolising enzymes (XMEs), the inhibition of bioactivating Phase-I XMEs and/or induction of detoxifying Phase-II XMEs being one of the most evoked cancer chemopreventive strategies. Here, several CYP-dependent oxidations were studied in liver sub-cellular preparations from Sprague-Dawley rats receiving rodent chow supplemented with folic acid daily, for 1 or 2 consecutive months. Using either specific substrates as probes of different CYP isoforms or the regio- and stereo-selective metabolism of testosterone as a multibiomarker, we found that folic acid markedly inactivated most of the Phase-I XME analysed; up to 54% for the CYP1A1-linked deethylation of ethoxyresorufin in males, and up to 86% for the testosterone 2alpha-hydroxylase (CYP2C11) in females, after 2 months treatment. The Phase-II marker glutathione S-transferase significantly increased (~107%) after 1 month of supplementation in females only. These changes, if reproduced in humans might have public health implications. These data suggest caution in performing folate chemoprevention trials before its overall toxicological characterization has been fully addressed.     

Glutathione depletion and anaesthesia in mice alter heme and drug metabolising enzymes

The effects of enflurane and isoflurane on heme metabolism, its regulation, and on some parameters involved in the hepatic drug metabolising system in animals under GSH depletion were investigated. A single dose of the anaesthethics (1 ml kg(-1), i.p.) was administered to control and GSH depleted mice, animals were sacrificed 20 min after. As a consequence of GSH depletion, a significant inhibition in delta-Aminolevulinic acid synthetase activity, the first enzyme of heme biosynthesis, and a striking induction in Heme oxygenase activity, the main enzyme of heme metabolism, were observed. Cytochrome P-450 levels and the activities of P-4502E1 and glutathione S-transferase were increased. These changes in heme metabolism and drug metabolising enzyme system were not altered further by the administration of enflurane or isoflurane. These findings would indicate that the status of oxidative stress produced by GSH depletion could not be affected by these anaesthetics and/or that disturbances in heme metabolism were already too important to undergo further variations.     

Xenobiotic metabolizing enzymes in the central nervous system: Contribution of cytochrome P450 enzymes in normal and pathological human brain

The metabolism of xenobiotics in human brain constitutes a field of recent intensive research in relation to the potential implications in the pharmacological effect of drugs acting on the central nervous system. Cytochrome P450 enzymes (CYPs) play a crucial role in these metabolic pathways and the existence of functional CYP monooxygenases in brain is now well established. These enzymes are preferentially localized in the neuronal cells within the microsomal fraction and the inner membrane of mitochondria. Although low, the metabolism in situ could influence individual response to xenobiotics or produce reactive, toxic metabolites causing irreversible damage in the neuronal cells. The abundant presence of CYPs in selective cell populations within different regions of the brain has also suggested a role for these enzymes in brain physiology thus not restricted to xenobiotic-induced neurotoxicity. For instance, CYPs participate in the regulation of neurotransmitters and steroids and brain maintenance of cholesterol homeostasis. Recent advances support an additional role for these enzymes in the pathogenesis of psychiatric and neurodegenerative disorders such as depression, schizophrenia, and Alzheimer's and Parkinson's diseases. The characterization of brain CYP isoforms and their localization, the identification of their substrates and metabolic end-products will allow better understanding of the role of these enzymes in brain physiology, development and diseases.     

Microphotometric determination of enzymes in brain sections. I. Hexokinase

A histochemical procedure was established for the microphotometric determination of hexokinase (HK) in sections of the rat hippocampus, which served as an exemplary brain region. For this quantitative procedure, slides were coated with glucose 6-phosphate dehydrogenase (G6PDH) as an auxiliary enzyme and sections were mounted onto this enzyme film. The sections were then incubated with the following adapted incubation medium: 5 mM D-glucose, 1.5 mM NADP, 7.5 mM ATP, 4 mM nitroblue tetrazolium chloride, 10 mM NaN3, 10 mM MgCl2, 0.25 mM phenazine methosulfate, 1 U/ml G6PDH, 22% polyvinyl alcohol in 0.05 M Hepes buffer; the final pH was 7.5. A linear response of the reaction was observed in the initial 10 min of reaction (kinetic and end-point measurements). The relationship between HK activity and section thickness was linear up to 5 microns. The need for such thin sections is discussed in relation to the limited penetration of the auxiliary enzyme into the section. It is concluded that the quantitative demonstration of HK in brain sections could be a valuable tool for studying the local metabolic entrance of glucose in the glycolytic pathway.     

Epigenetic regulation of carnitine metabolising enzymes in Proteus sp. under aerobic conditions

Proteus sp. is able to catalyse the reversible transformation of crotonobetaine into L(-)-carnitine during aerobic growth. Contrary to other Enterobacteriaceae no reduction of crotonobetaine into gamma-butyrobetaine could be detected in the culture supernatants. Activities of L(-)-carnitine dehydratase, carnitine racemasing system and crotonobetaine reductase could be determined enzymatically in cell-free extracts of Proteus sp. Small amounts of gamma-butyrobetaine were found in cell-free extracts, indicating that it accumulates in the cell and inhibits the crotonobetaine reductase. Crotonobetaine and L(-)-carnitine were able to induce enzymes of carnitine metabolism. gamma-Butyrobetaine and glucose repress carnitine metabolism in Proteus sp. Other betaines are neither inducers nor repressors. Monoclonal antibodies against purified CaiA from Escherichia coli O44K74 recognise an analogous protein in cell-free extract of Proteus sp. No cross-reactivity could be detected with monoclonal antibodies against purified CaiB and CaiD from E. coli O44K74.     

Antimutagenic effects of wheat bran diet through modification of xenobiotic metabolising enzymes

Diets containing wheat bran (WB) protect against cancers of the colon or breast in rats, and may be beneficial in humans. In a previous study of rats treated with the carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), inclusion of 10% wheat bran in the diet led to an apparent reduction in IQ metabolites but not of intact IQ in plasma. In the present study, male Wistar rats were fed diets containing 0, 10 or 20% wheat bran, and effects on xenobiotic metabolising enzymes compared. Wheat bran-supplementation showed differential effects on phase I enzymes, significantly increasing the activity of hepatic cytochrome P450 isozyme CYP3A2, but slightly reducing the activity of CYP1A1/2. The activities of both hepatic phase II detoxification enzymes glutathione-S-transferase and glucuronosyl transferase were also reduced. Western blotting revealed similar effects on expression of the proteins. Interestingly, the expression of xenobiotic metabolising enzymes (XME) in the colon appeared to be modulated independently of hepatic XME. Although the wheat bran-supplemented diet still led to an increased expression of CYP3A, it now slightly increased CYP1A in the colon. However, 20% wheat bran significantly increased the expression of both glutathione transferase isozymes, GST A1 & A2, in the colon. Natures Gold (NG) is a commercial wheat bran derivative which is lower than wheat bran in dietary fibre, but enriched in vitamins, minerals and various phytochemicals. Dietary supplementation with 20% Natures Gold led to similar trends as seen in wheat bran-fed rats, but more potent effects in both hepatic and colonic enzymes. The significance of these changes for activation of carcinogens to mutagenic metabolites was investigated using the Salmonella/mammalian microsome mutagenicity test. The activation of IQ and benzo[a]pyrene, but not cyclophosphamide, to a mutagen by hepatic S9 from wheat bran-fed or Natures Gold-fed rats was significantly reduced compared with S9 from animals on a diet lacking wheat bran. We suggest that modulation of xenobiotic metabolising enzymes may be an important component of cancer protection by wheat bran, and this effect may relate to micronutrients or cancer-protective non-nutrient phytochemicals rather more than to dietary fibre.     

Effect of plumbagin on some glucose metabolising enzymes studied in rats in experimental hepatoma

Plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone) isolated from Plumbago zeylanica Linn, when administered orally, at a dosage of 4 mg/kg body weight induces tumour regression in 3-methyl-4-dimethyl aminoazobenzene (3Me-DAB) induced hepatoma in Wistar male rats. The purpose of this investigation was to identify the changes in the rate of glycolysis and gluconeogenesis in tumour-bearing rats and the effects of treatment with Plumbagin. The levels of certain glycolytic enzymes, namely, hexokinase; phosphoglucoisomerase; and aldolase levels increased (p<0.001) in hepatoma bearing rats, whereas they decreased in Plumbagin administered rats to near normal levels. Certain gluconeogenic enzymes, namely, glucose-6-phosphatase and fructose-1,6-diphosphatase decreased (p<0.001) in tumour hosts, whereas Plumbagin administration increased the gluconeogenic enzyme levels in the treated animals. These investigations indicate the molecular basis of the different biological behaviour of 3MeDAB induced hepatoma and the anticarcinogenic property of Plumbagin against hepatoma studied in rats.     

Fructan metabolising enzymes in rhizophores of Vernonia herbacea upon excision of aerial organs.

The activities of fructan metabolising enzymes and fructan contents are reported for rhizophores of Vernonia herbacea (Vell.) Rusby induced to sprouting by shoot excision. The activities of fructan exohydrolase (1-FEH), sucrose: sucrose fructosyltransferase (1-SST), fructan: fructan fructosyltransferase (1-FFT) and invertase (INV) and the fructan contents were analysed every 3-4 days for 1 month by colorimetric and chromatographic methods. Sprouting of new shoots started on day 9. 1-FEH activity increased after day 13 and reached its maximum value 20 days after shoot excision. A gradual decrease in 1-SST activity was detected between days 3 and 9. 1-FFT activity exhibited fluctuations throughout the experimental period and a peak of activity for invertase was detected 9 days after shoot excision. Variation in fructan contents in vivo included a decrease until day 13 after which, levels remained practically unchanged. Fructan depolymerization and sprouting are concomitant processes in V. herbacea and can be induced by shoot excision at any phenological phase. 1-FEH and 1-FFT seemed to act in a concerted way to catalyse fructan depolymerization, while 1-SST was inhibited, possibly due to interruption of sucrose supply to rhizophores from the aerial organs.     

Microphotometric determination of enzymes in brain sections. II. GABA transaminase

The tetrazolium salt procedure of van Gelder (1965) for the demonstration of GABA transaminase (GABAT; the most important GABA degrading enzyme) was adapted for microphotometric measurements of GABAT activities in brain sections using the hippocampus of rats as selected brain region. The final incubation medium consisted of 50 mM GABA, 5 mM alpha-ketoglutarate, 7 mM NAD, 10 mM sodium azide, 6 mM nitroblue tetrazolium chloride, 20 mM malonate and 15% polyvinyl alcohol in 0.05 M Hepes buffer; the final pH was 8.0. There was a linear relationship between GABAT activity and section thickness up to 14 microns and between GABAT activity and reaction time at least up to 20 min (kinetic and end-point measurements). Phenazine methosulfate as an exogenous electron carrier and pyridoxal-5-phosphate as coenzyme of GABAT did not enhance the demonstrable GABAT activities, whereas sodium azide as a blocker of the respiratory chain resulted in an increase of demonstrable enzyme activities. A coreaction of succinate dehydrogenase was excluded by the use of malonate (competitive inhibitor). Using the incubation medium described GABAT activities were demonstrated via the endogenous enzymes succinic semialdehyde dehydrogenase and NADH tetrazolium reductase which were shown to be not rate limiting and seems to be similarly localized as GABAT.     

Microphotometric determination of enzymes in brain sections. IV. Isocitrate dehydrogenases

A polyvinyl alcohol-(PVA) containing incubation medium was adapted for the microphotometric determination (kinetic and end-point measurements) of the activities of NAD- and NADP-linked isocitrate dehydrogenases (ICDHs) in cryostat sections of the rat hippocampus. The following incubation medium is recommended for the quantification of NAD- and NADP- (differences in brackets) ICDHs: 100 mM DL-isocitrate, 10 mM sodium azide, 5 mM (4 mM) nitroblue tetrazolium (NBT), 7 mM NAD (4 mM NADP), 10 mM magnesium chloride, 0.25 mM phenazine methosulfate (PMS), with or without 5 mM ADP (without ADP), 23% PVA in 0.05 M Hepes buffer; the final pH was 7.5. With these incubation media a linear response of the reactions lasted at least 20 min. In kinetic and end-point measurements the same level of activities was demonstrable. The use of NaN3 (as a blocker of the respiratory chain) and PMS (as artificial electron carrier) was indispensible for the transfer of all reduction equivalents in the dehydrogenase reactions to the tetrazolium salt NBT. Furthermore, the activation by magnesium ions and the need of PVA to avoid diffusion artefacts of the loosely bound ICDHs were clearly shown. It is concluded that the quantification of ICDHs in situ could be a valuable tool for neurochemical investigations because ICDHs play a role not only in the substrate flux through the tricarboxylic acid cycle but also in providing alpha-ketoglutarate for the formation of glutamate which is an important amino acid in the brain.