Dehydroepiandrosterone, glucose-6-phosphate dehydrogenase, and longevity

Dehydroepiandrosterone (DHEA) is an abundantly produced adrenal steroid whose biological role has never been clarified. DHEA is a potent uncompetitive inhibitor of mammalian glucose-6-phosphate dehydrogenase (G6PDH) and as a consequence lowers NADPH levels and reduces NADPH-dependent oxygen-free radical production. Overproduction of oxygen-free radicals, or oxidative stress, upregulates inflammation and cellular proliferation and is believed to play a critical role in the development of cancer, atherosclerosis, and Alzheimer's disease, as well as the basic aging process. Both in vitro and in vivo experimental studies strongly indicate that DHEA and related steroids inhibit inflammation and associated epithelial hyperplasia, carcinogenesis, and atherosclerosis, at least in part, through the inhibition of G6PDH and oxygen-free radical formation. Recent epidemiological findings in Sardinian males bearing the Mediterranean variant of G6PDH deficiency are consistent with the hypothesis that reduced G6PDH activity has a beneficial effect on age-related disease development and longevity. Clinical trials with DHEA are encumbered by the high oral doses required as well as the conversion of DHEA into active androgens. The use of less androgenic congeners as well as non-oral formulations may facilitate testing of this class of compounds.     

Microphotometric study on cytochrome oxidase and lactate dehydrogenase activities in mouse spermatozoa during maturation and in vivo and in vitro capacitation

In Eutherian (mammalian) spermatozoa, maturation and capacitation are associated to modifications of the metabolic activities. In order to demonstrate such variations, a quantitative cytochemical study was carried out on cytochrome oxidase and L-lactate dehydrogenase activities in mouse spermatozoa collected from the male and female genital tracts and at different times of the in vitro capacitation. Microdensitometric measurements were made on a Vickers M85 integrator microdensitometer at lambda = 480 +/- 5 nm and lambda = 585 +/- 5 nm wavelengths for the cytochrome oxidase and LDH activities, respectively. The cytochrome oxidase activity first decreases and then increases significantly both during maturation and during capacitation in vivo and in vitro. The LDH activity decreases significantly and gradually in the male and female genital tracts as well as in the course of in vitro capacitation where, however, an enhancement in the anaerobic glycolysis occurs.     

Biology of glucose-6-phosphate dehydrogenase deficiency

G-6-PD deficiency is predominant in the entire history of haemolytic anemias secondary to enzyme deficiency, since its represents, by far, the most frequent erythro-enzymopathy; it is also the most studied and the best known from the clinical as well as biological standpoints. Because of the ethnic groups particularly affected, this deficiency is essentially, in France, an imported pathology, even if there are a few true european cases. The biological diagnosis of the deficient patient is simple and well codified, but the interpretation of numerous variants of the enzyme remains quite complex. The recent cloning of the gene should provide a decisive progress in understanding these various deficiencies.     

Ultracytochemistry of glucose-6-phosphate dehydrogenase in adrenal gland.

The distribution of glucose-6-phosphate dehydrogenase (G6PD) activity has been studied by a copper ferrocyanide method in the adrenal cortex cells of a rat. The site of the G6PDH activity was close to the ribosome between the round mitochondria of zonas fasciculata and reticularis.     

Microphotometric study of glucose-6-phosphate dehydrogenase activity in epididymal spermatozoa during spontaneous lipid peroxidation

Mammalian spermatozoa are highly sensitive to lipid peroxidation and the glutathione peroxidase/reductase system provides an effective defense against oxidative damage to different degree in different species. Rabbit spermatozoa rely on superoxide dismutase as the primary enzymatic defense against lipid peroxidation and contain only low detectable endogenous glutathione reductase activity while in mouse spermatozoa the glutathione system is the major protective enzyme against cell damage by autoxidation. We describe a cytochemical quantitative assay for glucose-6-phosphate dehydrogenase activity in rabbit and mouse spermatozoa undergoing spontaneous lipid peroxidation during in vitro incubation. Microdensitometric measurements were made by a Vickers M85 a scanning microdensitometer at lambda 585 nm wavelength. Our findings suggest that in mouse spermatozoa, the enhanced glutathione reductase and peroxidase activities induced by the spontaneous lipid peroxidation increases NADPH production from the pentose phosphate shunt, while in rabbit spermatozoa, NADPH production is much lower.     

Examination of HeLa cell contamination of human cell lines derived from primary hepatomas using glucose-6-phosphate dehydrogenase and lactate dehydrogenase isozymes

Isozyme patterns of glucose-6-phosphate dehydrogenase (G6PD) and lactate dehydrogenase (LDH) in human cell lines derived from primary hepatomas were compared with those in HeLa cells. Some cell lines derived from primary hepatomas having type B G6PD showed one or two isozymes of LDH. On the other hand, HeLa cells having type A G6PD showed four LDH isozymes. These findings suggest that not only G6PD, but also LDH may be useful for the detection of HeLa cell contamination of a culture in some cases.     

Characterization of glucose-6-phosphate dehydrogenase isozymes from human and pig brain

Homogenates of human and pig brain in 10 mM Tris-HCl, pH 8.0 were centrifuged at 25,400 x g for 1 h. The supernatants were electrophoresed in polyacrylamide gels were stained for glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity. Five distinct bands were visible. Isozymes corresponding to two of those bands were purified from human and pig brain. The isozymes were electrophoretically homogeneous. The native proteins, Mr, 220,000, dissociated in sodium dodecyl sulphate-polyacrylamide gels into a 57,000 Mr subunit. Therefore, the native isozymes are tetramers. None of the isozymes required additional metal ions for activity. At 1 mM concentration Mg2+ and Ca2+, independently or together, activated the isozymes 1.5-fold. The isozymes were NADP(+)-specific. Kmapp values of the G6PD isozymes were similar for NADP+ (6-8 microM), but different for G6P (56-180 microM). The specific activities of the isozymes varied from 50 to 210 units per mg of protein. All isozymes were inhibited by NADPH. The inhibition was competitive with respect to NADP+ and non-competitive with respect to G6P. NADH did not affect any of the isozymes. ATP inhibited the isozymes competitively with respect to G6P and non-competitively with respect to NADP+. Palmitoyl-CoA dissociated the active tetramers into enzymatically inactive dimeric forms. This treatment also abolished the 6-phosphogluconate activity of the isozyme II from both sources. High performance liquid chromatography peptide maps of the tryptic digest and amino acid analyses of the isozymes showed extensive homologies between the corresponding isozymes from the two species. Interestingly, only the isozyme II in human and pig brain was active with 6-phosphogluconate as a substrate (Kmapp = 864 and 279 microM). The specific activities of the isozyme II with 6-phosphogluconate (14 and 48 unit per mg of protein for human and pig brain isozyme II, respectively) was four times less than those with G6P. It is therefore suggested that isozyme II is a bifunctional enzyme.     

Studies on glucose-6-phosphate dehydrogenase from the human parasite,Onchocerca volvulus

Glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) was partially purified from the extracts of adult Onchocerca volvulus by affinity chromatography on 25ADP-Sepharose-4B. Kinetic studies revealed a typical bell-shaped pH profile with an optimum lying between pH 7.3 and 7.8. The apparent K_m for glucose-6-phosphate was 5.66×10^–5 M, whereas that for NADP was 2.17×10^–6 M. Suramin, a filaricidal drug, inhibited the enzyme competitively with respect to NADP as a substrate: the apparent K_i values were 2.23×10^–6 M and 4.21×10^–7 M, respectively, for the crude and purified enzyme preparations. Glucose-6-phosphate dehydrogenase therefore, could be one of the targets of suramin in vivo.     

G6PD缺乏症发病的分子病理学新机制

葡萄糖-6-磷酸脱氢酶缺乏症(gluocose-6-phosphate dehydrogenase deficiency,简称G6PD缺乏症)是人类最常见的酶缺陷遗传病之一,全球约有4亿多人受累.G6 PD缺乏症主要是由于G6PD基因发生变异所引起,其经典分子病理学机制研究主要集中在G6PD基因的突变研究上,但对少部分病例来说,经典的发病机制并不能对其表型和基因型的关系作出合理的解释.近些年来,一些学者在G6PD缺乏症发病新的分子机制方面作了较为深入的研究,为了更好的理解本病,该文就近年来对于G6PD缺乏症发病的分子病理学新机制的研究作一综述.     

Glucokinase,hexokinase, and glucose-6-phosphate dehydrogenase activities in the livers and myocardia of rabbits with pyrogenal-induced fever

Glucokinase, hexokinase, and glucose-6-phosphate dehydrogenase activities of the liverand myocardium were studied in experiments on rabbits in various stages of pyrogenal-induced fever. Activity of the first stage of glycolysis was found to be depressed. In the postfebrile period, activities of these enzymes returned to normal.Department of Pathological Physiology, Kalinin Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR P. N. Veselkin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 2, pp. 181–182, February, 1976.     

Detection of a new abnormal variant of glucose-6-phosphate dehydrogenase in human erythrocytes

The kinetic and electrophoretic properties of preparations of glucose-6-phosphate dehydrogenase (G6PD), obtained from erythrocytes from healthy blood donors and patients with acute drug-induced hemolytic anemia caused by G6PD deficiency, purified 230–300 times, were investigated. A new abnormal variant of G6PD, not previously described in the literature, was isolated from the erythrocytes of a patient with acute drug-induced hemolytic anemia. The abnormal enzyme differs from the normal in having a lower Michaelis constant for glucose-6-phosphate and NADP, in its increased utilization of substrate analogs (2-deoxyglucose-6-phosphate and, in particular, diamino-NADP), low thermostability, the character of its pH dependence, and in the appearance of only one band of G6PD activity during electrophoresis in polyacrylamide gel.Central Institute of Hematology and Blood Transfusion, Ministry of Health of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR S. E. Severin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 84, No. 12, pp. 728–731, December, 1977.