Stress, hormonal changes, alcohol, food constituents and drugs: factors that advance the incidence of tobacco smoke-related cancer?

Effects of nicotine and vitamin E on glucose 6-phosphate dehydrogenase activity in some rat tissuesin vivoandin vitro

Effects of nicotine, and nicotine + vitamin E on glucose 6-phosphate dehydrogenase (G-6PD) activity in rat muscle, heart, lungs, testicle, kidney, stomach, brain and liver were investigated in vivo and in vitro on partially purified homogenates. Supplementation period was 3 weeks (n = 8 rats per group): nicotine [0.5 mg/kg/day, intraperitoneal (ip)]; nicotine + vitamin E [75 mg/kg/day, intragastric (ig)]; and control group (receiving only vehicle). The results showed that nicotine (0.5 mg/kg, ip) inhibited G-6PD activity in the lungs, testicle, kidney, stomach and brain by 12.5% (p < 0.001), 48% (p < 0.001), 20.8% (p < 0.001), 13% (p < 0.001) and 23.35% (p < 0.001) respectively, and nicotine had no effects on the muscle, heart and liver G6PD activity. Also, nicotine + vitamin E inhibited G-6PD activity in the testicle, brain, and liver by 32.5% (p < 0.001), 21.5% (p < 0.001), and 16.5% (p < 0.001) respectively, and nicotine + vitamin E activated the muscle, and stomach G-6PD activity by 36% (p < 0.05), and 20% (p < 0.001) respectively. In addition, nicotine + vitamin E did not have any effects on the heart, lungs, and kidney G-6PD activity. In addition, in vitro studies were also carried out to elucidate the effects of nicotine and vitamin E on G-6PD activity, which correlated well with in vivo experimental results in lungs, testicles, kidney, stomach, brain and liver tissues. These results show that vitamin E administration generally restores the inactivation of G-6PD activity due to nicotine administration in various rat tissues in vivo, and also in vitro.

Effects of nicotine and Vitamin E on Carbonic anhydrase activity in some rat tissues In Vivo and In Vitro

Effects of nicotine, nicotine + vitamin E and nicotine + Hippophea rhamnoides L. extract (HRe-1) on muscle, heart, lungs, testicle, kidney, stomach, brain and liver carbonic anhydrase (CA; EC 4.2.1.1.) enzyme activities were investigated in vivo. Groups of rats were given nicotine (0.5 mg/kg/day, i.p.), nicotine + vitamin E (75 mg/kg/day, i.g.), nicotine + HRe-1 (250 mg/kg/day, i.g.) and a control group vehicle only. The results showed that nicotine inhibited the heart, lung, stomach and liver CA enzyme activities by approximately 80% (p < 0.001), approximately 94% (p < 0.001), approximately 47% (p < 0.001) and approximately 81% (p < 0.001) respectively, and activated muscle and kidney, but had no effects on the testicle and brain CA activities. Nicotine + vitamin E inhibited the heart and liver CA enzyme activities by approximately 50% (p < 0.001), and approximately 50% (p < 0.001), respectively, and nicotine + vitamin E activated the muscle CA activity. However, nicotine + vitamin E had no effect on lung, testicle, kidney, stomach and brain CA activities. Nicotine + HRe-1 inhibited the heart and stomach CA enzyme activities by approximately 51% (p < 0.001), and approximately 32% (p < 0.002), respectively, and activated the muscle and brain CA activities, but had no effects on the lung, testicle, kidney, and liver CA activities. In vitro CA inhibition results for similar experiments correlated well with the in vivo experimental results in lungs, testicles, kidney, stomach, brain and liver tissues.

Carbonyl reductases: the complex relationships of mammalian carbonyl- and quinone-reducing enzymes and their role in physiology

Carbonyl groups are frequently found in endogenous or xenobiotic compounds. Reactive carbonyls, formed during lipid peroxidation or food processing, and xenobiotic quinones are able to covalently modify DNA or amino acids. They can also promote oxidative stress, the products of which are thought to be an important initiating factor in degenerative diseases or cancer. Carbonyl groups are reduced by an array of distinct NADPH-dependent enzymes, belonging to several oxidoreductase families. These reductases often show broad and overlapping substrate specificities and some well-characterized members, e.g., carbonyl reductase (CBR1) or NADPH-quinone reductase (NQO1) have protective roles toward xenobiotic carbonyls and quinones because metabolic reduction leads to less toxic products, which can be further metabolized and excreted. This review summarizes the current knowledge on structure and function relationships of the major human and mammalian carbonyl reductases identified.

Purification, characterization and NNK carbonyl reductase activities of 11beta-hydroxysteroid dehydrogenase type 1 from human liver: enzyme cooperativity and significance in the detoxification of a tobacco-derived carcinogen

11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) physiologically catalyzes the interconversion of receptor-active 11-hydroxy glucocorticoids (cortisol) to their receptor-inactive 11-oxo metabolites (cortisone), thereby acting as important pre-receptor control device in regulating access of glucocorticoid hormones to the glucocorticoid receptor. Evidence is emerging that 11beta-HSD 1 fulfills an additional role in the detoxification of non-steroidal carbonyl compounds, by catalyzing their reduction to the corresponding hydroxy derivatives that are easier to conjugate and eliminate. Whereas a number of methods were ineffective in purifying 11beta-HSD 1 from human liver, this membrane-bound enzyme was successfully obtained in an active state by a purification procedure that took advantage of a gentle solubilization method as well as providing a favourable detergent surrounding during the various chromatographic steps. We could demonstrate that 11beta-HSD 1 is active as a dimeric enzyme which exhibits cooperativity with cortisone and dehydrocorticosterone (11-oxoreducing activity) as substrates. Accordingly, this enzyme dynamically adapts to low (nanomolar) as well as to high (micromolar) substrate concentrations, thereby providing the fine tuning required as a consequence of great variations in circadian plasma glucocorticoid levels. Due to this kinetic peculiarity, 11beta-HSD 1 is also able to even metabolize nanomolar concentrations of the tobacco-specific nitrosamine 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK), a fact which is important in view of the relatively low levels of this carcinogen observed in smokers. Finally, 11beta-HSD 1 is potently (in nM concentrations) inhibited by glycyrrhetinic acid, the main constituent of licorice. Licorice, however, in addition to being a confectionary, serves as a major cigarette additive, which is used in cigarette manufacturing as a taste and flavour intensifier. Hence, licorice exposure may affect NNK detoxification by inhibition of 11beta-HSD 1, a condition which may advance lung cancer incidence, especially in smokers expressing low levels of this enzyme. Collectively, our data expand insights into the multifunctional nature of hydroxysteroid dehydrogenases/carbonyl reductases and emphasize the importance of 11beta-HSD 1 in the detoxification of a tobacco-derived carcinogen, in addition to its endocrinological functions.

Enzymology and Molecular Biology of Glucocorticoid Metabolism in Humans

Glucocorticoids (GCs) are a vital class of steroid hormones that are secreted by the adrenal cortex and that are regulated by ACTH largely under the control of the hypothalamic-pituitary-adrenal axis. GCs mediate profound and diverse physiological effects in vertebrates, ranging from development, metabolism, neurobiology, anti-inflammation and programmed cell death to many other fuctions. Multiple factors "downstream" of GC secretion, such as glucocorticoid receptor (GR) number and the abundance of plasma binding proteins have originally been considered as modulators of GC action. However, in the last decade the role of tissue-specific GC activating and inactivating enzymes have been identified as additional determinants in GC signalling pathways. On the cellular level, they function as important pre-receptor regulators by acting as "molecular switches" for receptor-active and receptor-inactive GC hormones. According to their biologic activity to catalyze the interconversion of C11-hydroxyl and C11-oxo GCs these enzymes have been named 11beta-hydroxysteroid dehydrogenase (11beta-HSD; EC 1.1.1.146). Two isoforms of 11beta-HSD have been cloned and characterized so far. 11beta-HSD type 1 is found in a wide range of tissues, acts predominantly as a reductase in intact cells and tissues by regenerating active cortisol from cortisone, and has been described to regulate GC access to the GR. 11beta-HSD type 2 is found mainly in mineralocorticoid target tissues such as kidney and colon, acts only as a dehydrogenase by producing inactive cortisone, and has been found to protect the mineralocorticoid receptor from high levels of receptor-active cortisol. Recently, 11beta-HSD 1 has become highly topical due to the finding that 11beta-HSD 1 plays a pivotal role in the pathogenesis of central obesity and the appearance of the metabolic syndrome. This review provides an overview on the components involved in GC signalling of 11beta-HSD type 1 as an important pre-receptor control enzyme that modulates activation of the GR.

Expression and NNK reducing activities of carbonyl reductase and 11beta-hydroxysteroid dehydrogenase type 1 in human lung

The tobacco specific nitrosamine 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK), which is found in high amounts in tobacco products, is believed to play an important role in lung cancer induction in smokers. NNK requires metabolic activation by cytochrome P450 mediated alpha-hydroxylation to exhibit its carcinogenic properties. On the other hand, NNK is inactivated by carbonyl reduction to its alcohol-equivalent 4-methylnitrosamino-1-(3-pyridyl)-1-butanol (NNAL) followed by glucuronidation and final excretion into urine or bile. Carbonyl reduction and alpha-hydroxylation are the predominant pathways in man, and it has been postulated that the extent of these competing pathways determines the individual susceptibility to lung cancer. Moreover, only a minor part of all habitual smokers develop lung cancer, suggesting the existence of susceptibility genes. Microsomal 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) (EC 1.1.1.146) and cytosolic carbonyl reductase (CR) (EC 1.1.1.184) have been shown to be mainly responsible for NNAL formation in liver and lung. In the present study, we performed comparative investigations of human lung tissue samples from several patients with respect to the expression and activity of 11beta-HSD 1 and carbonyl reductase. We observed varying levels in 11beta-HSD 1 and carbonyl reductase expression in these patients, as revealed by RT-PCR and ELISA. Also, the tissue samples showed a different activity and inhibitor profile for both enzymes. According to our results, variations in the expression and activity of NNK carbonyl reducing enzymes may constitute a major determinant in the overall NNK detoxification capacity and thus may be linked to the great differences observed in the individual susceptibility of tobacco-smoke related lung cancer.

Molecular and structural aspects of xenobiotic carbonyl metabolizing enzymes. Role of reductases and dehydrogenases in xenobiotic phase I reactions

The major metabolic pathways involved in synthesis and disposition of carbonyl and hydroxyl group containing compounds are presented, and structural and functional characteristics of the enzyme families involved are discussed. Alcohol and aldehyde dehydrogenases (ADH, ALDH) participate in oxidative pathways, whereas reductive routes are accomplished by members of the aldo-keto reductase (AKR), short-chain dehydrogenases/reductases (SDR) and quinone reductase (QR) superfamilies. A wealth of biochemical, genetic and structural data now establishes these families to constitute important phase I enzymes.

Interindividual variability in the expression and NNK carbonyl reductase activity of 11beta-hydroxysteroid dehydrogenase 1 in human lung

The balance between metabolic activation and detoxification is critical in determining the susceptibility to lung cancer upon exposure to the tobacco specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Carbonyl reduction of NNK, followed by glucuronidation, is the main detoxification pathway of this lung carcinogen in humans. Recently, we have identified 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) as microsomal NNK carbonyl reductase in liver and lung. In the present study, the interindividual variability of 11beta-HSD 1 expression and NNK-carbonyl reductase activity was examined in human lung by RT-PCR, Western blot analysis and enzyme activity. Levels of 11beta-HSD 1 mRNA varied over an almost 20-fold range among different subjects. Levels of NNK carbonyl reductase activity in lung microsomes closely resembled the relative amounts of immunoreactive protein as determined by Western blot analysis. In view of the large interindividual differences in the susceptibility of tobacco smoke related lung cancer, we present the first data on the variability of 11beta-HSD 1 expression and NNK carbonyl reduction in human lung.

Preferential effects of nicotine and 4-(N-methyl-N-nitrosamine)-1-(3-pyridyl)-1-butanone on mitochondrial glutathione S-transferase A4-4 induction and increased oxidative stress in the rat brain

We have investigated the in vivo effects of the tobacco-specific toxins nicotine and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on antioxidant defense systems in the mitochondrial, microsomal, and cytosolic compartments of rat brain, lung, and liver. Nicotine induced maximum oxidative stress in brain mitochondria, as seen from a 1.9-fold (P < 0.001) increase in thiobarbituric acid-reactive substance (TBARS) and a 2-fold (P < 0.001) increase in glutathione S-transferase (GST) A4-4 (also referred to as rGST 8-8) activities. These changes were accompanied by a 25-40% increase in reactive oxygen species and a 20-30% decrease in alcohol dehydrogenase activities. The 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone-induced oxidative damage was apparent in the microsomal fraction of brain, lung, and liver, and it also increased 4-hydroxynonenal specific GST A4-4 activity in the brain and lung mitochondrial matrix fraction. The levels of microsomal thiobarbituric acid reactive substance, cytochrome P4502E1 activity, and reactive oxygen species were also increased significantly (P < 0.001) in all tissues. Both of these toxins induced the level of GST A4-4 mRNA in the brain, while they caused a marked reduction in the liver GST A4-4 mRNA pool. Additionally, the brain mitochondrial matrix showed a markedly higher level of 4-hydroxynonenal specific GST activity and mGST A4-4 antibody-reactive protein than did the cytosolic fraction. In conclusion, the present study provides evidence for the occurrence of GST A4-4 enzyme activity in mammalian mitochondria, in addition to demonstrating that both mitochondria and microsomes are intracellular targets for nicotine- and NNK-induced organ toxicity.