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

Modulation by Ozone of Glucocorticoid-Regulating Factors in the Lungs in Relation to Stress Axis Reactivity

Exposure to air pollutants increases levels of circulating glucocorticoid stress hormones that exert profound effects relevant to health and disease. However, the nature and magnitude of tissue-level effects are modulated by factors that regulate local glucocorticoid activity; accordingly, inter-individual differences could contribute to susceptibility. In the present study, we characterized effects of ozone (O₃) inhalation on glucocorticoid-regulating factors in the lungs of rat strains with contrasting hypothalamic–pituitary–adrenal stress axis responses. Hyper-responsive Fischer (F344) and less responsive Lewis (LEW) rats were exposed to air or 0.8 ppm O₃ for 4 h by nose-only inhalation. Levels of the high-specificity and -affinity corticosteroid-binding globulin protein increased in the lungs of both strains proportional to the rise in corticosterone levels following O₃ exposure. Ozone reduced the ratio of 11β-hydroxysteroid dehydrogenase type 1 (HSDB1)/HSDB2 mRNA in the lungs of F344 but not LEW, indicating strain-specific transcriptional regulation of the major glucocorticoid metabolism factors that control tissue-level action. Intercellular adhesion molecule (ICAM)-1 and total elastase activity were increased by O₃ in both strains, consistent with extravasation and tissue remodeling processes following injury. However, mRNA levels of inflammatory markers were significantly higher in the lungs of O₃-exposed LEW compared to F344. The data show that strain differences in the glucocorticoid response to O₃ are accompanied by corresponding changes in regulatory factors, and that these effects are collectively associated with a differential inflammatory response to O₃. Innate differences in glucocorticoid regulatory factors may modulate the pulmonary effects of inhaled pollutants, thereby contributing to differential susceptibility.

Carbonyl reduction of NNK by recombinant human lung enzymes: identification of HSD17β12 as the reductase important in (R)-NNAL formation in human lung

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the most abundant and carcinogenic tobacco-specific nitrosamine in tobacco and tobacco smoke. The major metabolic pathway for NNK is carbonyl reduction to form the (R) and (S) enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) which, like NNK, is a potent lung carcinogen. The goal of this study was to characterize NNAL enantiomer formation in human lung and identify the enzymes responsible for this activity. While (S)-NNAL was the major enantiomer of NNAL formed in incubations with NNK in lung cytosolic fractions, (R)-NNAL comprised ~60 and ~95% of the total NNAL formed in lung whole cell lysates and microsomes, respectively. In studies examining the role of individual recombinant cytosolic reductase enzymes in lung NNAL enantiomer formation, AKR1C1, AKR1C2, AKR1C3, AKR1C4 and CBR1 all exhibited (S)-NNAL-formation activity. To identify the microsomal enzymes responsible for (R)-NNAL formation, 28 microsomal reductase enzymes were screened for expression by real-time PCR in normal human lung. HSD17β6, HSD17β12, KDSR, NSDHL, RDH10, RDH11 and SDR16C5 were all expressed at levels ≥HSD11β1, the only previously reported microsomal reductase enzyme with NNK-reducing activity, with HSD17β12 the most highly expressed. Of these lung-expressing enzymes, only HSD17β12 exhibited activity against NNK, forming primarily (>95%) (R)-NNAL, a pattern consistent with that observed in lung microsomes. siRNA knock-down of HSD17β12 resulted in significant decreases in (R)-NNAL-formation activity in HEK293 cells. These data suggest that both cytosolic and microsomal enzymes are active against NNK and that HSD17β12 is the major active microsomal reductase that contributes to (R)-NNAL formation in human lung.

Knockdown of the differentially expressed gene TNFRSF12A inhibits hepatocellular carcinoma cell proliferation and migration in vitro

Human hepatocellular carcinoma (HCC) has been reported to be highly insensitive to conventional chemotherapy. In the current study, the Agilent Whole Human Genome Oligo Microarray (4×44 K) was used in order to identify the differentially expressed genes between HCC and adjacent tissues, and the top 22 differentially expressed genes were confirmed through reverse transcription-quantitative polymerase chain reaction. Among the identified differences in gene expression, expression of tumor necrosis factor receptor superfamily member 12A (TNFRSF12A) was markedly higher in HCC tissue than in adjacent tissue. Previous studies have suggested that TNFRSF12A may serve a role in tumor growth and metastasis, thus in the current study, TNFRSF12A was knocked down in the SMMC7721 cell line through siRNA. This demonstrated that cells exhibited reduced reproductive and metastatic capacity ex vivo. Thus, the results of the current study suggest that TNFRSF12A may be a candidate therapeutic target for cancer including HCC, and additional genes that exhibited significantly different expression from normal adjacent tissues require further study.

11β-hydroxysteroid dehydrogenases: intracellular gate-keepers of tissue glucocorticoid action

Glucocorticoid action on target tissues is determined by the density of "nuclear" receptors and intracellular metabolism by the two isozymes of 11β-hydroxysteroid dehydrogenase (11β-HSD) which catalyze interconversion of active cortisol and corticosterone with inert cortisone and 11-dehydrocorticosterone. 11β-HSD type 1, a predominant reductase in most intact cells, catalyzes the regeneration of active glucocorticoids, thus amplifying cellular action. 11β-HSD1 is widely expressed in liver, adipose tissue, muscle, pancreatic islets, adult brain, inflammatory cells, and gonads. 11β-HSD1 is selectively elevated in adipose tissue in obesity where it contributes to metabolic complications. Similarly, 11β-HSD1 is elevated in the ageing brain where it exacerbates glucocorticoid-associated cognitive decline. Deficiency or selective inhibition of 11β-HSD1 improves multiple metabolic syndrome parameters in rodent models and human clinical trials and similarly improves cognitive function with ageing. The efficacy of inhibitors in human therapy remains unclear. 11β-HSD2 is a high-affinity dehydrogenase that inactivates glucocorticoids. In the distal nephron, 11β-HSD2 ensures that only aldosterone is an agonist at mineralocorticoid receptors (MR). 11β-HSD2 inhibition or genetic deficiency causes apparent mineralocorticoid excess and hypertension due to inappropriate glucocorticoid activation of renal MR. The placenta and fetus also highly express 11β-HSD2 which, by inactivating glucocorticoids, prevents premature maturation of fetal tissues and consequent developmental "programming." The role of 11β-HSD2 as a marker of programming is being explored. The 11β-HSDs thus illuminate the emerging biology of intracrine control, afford important insights into human pathogenesis, and offer new tissue-restricted therapeutic avenues.

Carbonyl reduction of bupropion in human liver

Bupropion is metabolized extensively in humans by oxidative and reductive processes. CYP2B6 mediates oxidation of bupropion to hydroxybupropion, but the enzyme(s) catalyzing carbonyl reduction of bupropion to erythro- and threohydrobupropion in human liver is unknown. The objective of this study was to examine the enzyme kinetics of bupropion reduction in human liver. In human liver cytosol, the reduction of bupropion to erythro-and threohydrobupropion was NADPH dependent with Cl(int) values of 0.08 and 0.60 µL·min(-1)mg(-1) protein, respectively. Bupropion reduction in liver microsomes was also NADPH dependent with Cl(int) values of 10.4 and 280 µL·min(-1)mg(-1) protein, respectively. Formation of erythro-and threohydrobupropion in microsomes exceeded that in cytosol by 70 and 170 fold, respectively. Menadione, an inhibitor of cytosolic carbonyl reducing enzymes (e.g. CBRs), inhibited erythro-and threohydrobupropion formation in cytosol with IC(50) of 30 and 54 µM, respectively. In microsomes 18β-glycyrrhetinic acid, an inhibitor of microsomal carbonyl reductases (e.g. 11β-HSDs), inhibited their formation with IC(50) of 25 and 26 nM, respectively. Our findings, in agreement with recent human placental studies, show that carbonyl reducing enzymes in hepatic microsomes are significant players in bupropion reduction. Contrary to past studies, we found that threohydrobupropion (not hydroxybupropion) is the major microsomal generated hepatic metabolite of bupropion.

Genetic variability in the metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL)

Urinary metabolites of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides, termed total NNAL, have recently been shown to be good predictors of lung cancer risk, years before diagnosis. We sought to determine the contribution of several genetic polymorphisms to total NNAL output and inter-individual variability. The study subjects were derived from the Harvard/Massachusetts General Hospital Lung cancer case-control study. We analyzed 87 self-described smokers (35 lung cancer cases and 52 controls), with urine samples collected at time of diagnosis (1992-1996). We tested 82 tagging SNPs in 16 genes related to the metabolism of NNK to total NNAL. Using weighted case status least squares regression, we tested for the association of each SNP with square-root (sqrt) transformed total NNAL (pmol per mg creatinine), controlling for age, sex, sqrt packyears and sqrt nicotine (ng per mg creatinine). After a sqrt transformation, nicotine significantly predicted a 0.018 (0.014, 0.023) pmol/mg creatinine unit increase in total NNAL for every ng/mg creatinine increase in nicotine at p < 10E-16. Three HSD11B1 SNPs and AKR1C4 rs7083869 were significantly associated with decreasing total NNAL levels: HSD11B1 rs2235543 (p = 4.84E-08) and rs3753519 (p = 0.0017) passed multiple testing adjustment at FDR q = 1.13E-05 and 0.07 respectively, AKR1C4 rs7083869 (p = 0.019) did not, FDR q = 0.51. HSD11B1 and AKR1C4 enzymes are carbonyl reductases directly involved in the single step reduction of NNK to NNAL. The HSD11B1 SNPs may be correlated with the functional variant rs13306401 and the AKR1C4 SNP is correlated with the enzyme activity reducing variant rs17134592, L311V.

The glucocorticoid-activating enzyme 11beta-hydroxysteroid dehydrogenase type 1 has broad substrate specificity: Physiological and toxicological considerations

The primary function of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is to catalyze the conversion of inactive to active glucocorticoid hormones and to modulate local glucocorticoid-dependent gene expression. Thereby 11beta-HSD1 plays a key role in the regulation of metabolic functions and in the adaptation of the organism to energy requiring situations. Importantly, elevated 11beta-HSD1 activity has been associated with metabolic disorders, and recent investigations with rodent models of obesity and type 2 diabetes provided evidence for beneficial effects of 11beta-HSD1 inhibitors, making this enzyme a promising therapeutic target. Several earlier and recent studies, mainly performed in vitro, revealed a relatively broad substrate spectrum of 11beta-HSD1 and suggested that this enzyme has additional functions in the metabolism of some neurosteroids (7-oxy- and 11-oxyandrogens and -progestins) and 7-oxysterols, as well as in the detoxification of various xenobiotics that contain reactive carbonyl groups. While there are many studies on the effect of inhibitors on cortisone reduction and circulating glucocorticoid levels and on the transcriptional regulation of 11beta-HSD1 in obesity and diabetes, only few address the so-called alternative functions of this enzyme. We review recent progress on the biochemical characterization of 11beta-HSD1, with a focus on cofactor and substrate specificity and on possible alternative functions of this enzyme.

Stimulation of 11β-HSD1 expression by IL-1β via a C/EBP binding site in human fetal lung fibroblasts

Proinflammatory cytokines, just like glucocorticoids (GCs), have been reported to upregulate 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expression in many cell types. This concerted regulation of 11β-HSD1 by interleukin-1β (IL-1β) and GCs is in marked contrast to their antagonistic effects on inflammation. Further, the molecular mechanisms underlying the induction of 11β-HSD1 by IL-1β are not very well understood. In this study, we demonstrated that IL-1β dramatically stimulated 11β-HSD1 expression and enzyme activity as well as promoter activity including the -64 bp fragment upstream to the transcription start site in human fetal lung fibroblasts (HFL-1). Nucleotide mutations of the proximal CCAAT box within this region abolished the induction of 11β-HSD1 promoter activity by IL-1β. Western blotting analysis demonstrated that IL-1β induced the expression of C/EBPβ dramatically while C/EBPα was barely detectable in HFL-1 cells. Global inhibition of CCAAT/enhancer-binding proteins (C/EBPs) with transfection of C/EBP-specific dominant-negative expression plasmid (CMV500-A-C/EBP) significantly attenuated the induction of 11β-HSD1 by IL-1β, whereas over-expression of C/EBPβ enhanced the expression of 11β-HSD1. Chromatin immunoprecipitation assay revealed the recruitment of C/EBPβ to the promoter region containing the C/EBP binding site. In conclusion, IL-1β induces the expression of 11β-HSD1 mRNA in the fetal lung tissue through mechanisms that involve C/EBPβ binding to the promoter. This impact of IL-1β on the expression of 11β-HSD1 in human fetal lung cells may explain the alternate mechanism for the lung maturation that appears to occur when there is a risk of premature delivery of the fetus due to the presence of infection.

Human cyt P450 mediated metabolic toxicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) evaluated using electrochemiluminescent arrays

Electrochemiluminescent (ECL) arrays containing polymer ([Ru(bpy)(2)(PVP)(10)](2+), PVP = polyvinylpyridine), DNA, and selected enzymes were employed to elucidate cytochrome (cyt) P450 dependent metabolism of the tobacco specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Bioactivated NNK metabolites formed upon H(2)O(2)-enzymatic activation were captured as DNA adducts and detected simultaneously from 36 spot arrays by capturing and quantifying emitted ECL with an overhead CCD camera. Increased ECL emission was dependent on NNK exposure time. Of the enzymes tested, the activity toward NNK bioactivation was cyt P450 1A2 > 2E1 > 1B1 approximately chloroperoxidase (CPO) > myoglobin (Mb) in accordance with reported in vivo studies. Cyt P450/polyion films were also immobilized on 500 nm diameter silica nanospheres for product analysis by LC-MS. Analysis of the nanosphere film reaction media provided ECL array validation and quantitation of the bioactivated NNK hydrolysis product 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) confirming production of reactive metabolites in the films. Chemical screening in this fashion allows rapid clarification of enzymes responsible for genotoxic activation as well as offering insight into cyt P450-related toxicity and mechanisms.

Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily

Carbonyl reduction of aldehydes, ketones, and quinones to their corresponding hydroxy derivatives plays an important role in the phase I metabolism of many endogenous (biogenic aldehydes, steroids, prostaglandins, reactive lipid peroxidation products) and xenobiotic (pharmacologic drugs, carcinogens, toxicants) compounds. Carbonyl-reducing enzymes are grouped into two large protein superfamilies: the aldo-keto reductases (AKR) and the short-chain dehydrogenases/reductases (SDR). Whereas aldehyde reductase and aldose reductase are AKRs, several forms of carbonyl reductase belong to the SDRs. In addition, there exist a variety of pluripotent hydroxysteroid dehydrogenases (HSDs) of both superfamilies that specifically catalyze the oxidoreduction at different positions of the steroid nucleus and also catalyze, rather nonspecifically, the reductive metabolism of a great number of nonsteroidal carbonyl compounds. The present review summarizes recent findings on carbonyl reductases and pluripotent HSDs of the SDR protein superfamily.

The tobacco carcinogen NNK is stereoselectively reduced by human pancreatic microsomes and cytosols

BACKGROUND/AIMS

Cigarette smoking increases the risk of cancer of the pancreas. The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the only known environmental compound that induces pancreatic cancer in laboratory animals. Concentrations of NNK are significantly higher in the pancreatic juice of smokers than in that of nonsmokers. The chiral NNK metabolite, (R,S)-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is itself a potent pancreatic carcinogen in rats. The carcinogenicity of NNAL is related to its stereochemistry; (S)-NNAL is a more potent lung tumorigen in the A/J mouse than is (R)-NNAL. In this study, we determined the potential of the human pancreas to convert NNK into NNAL.

MATERIALS AND METHODS

Human pancreatic microsomes and cytosols were incubated with [5-(3)H]NNK, and the metabolic products were determined by high-performance liquid chromatography (HPLC).

RESULTS

(S)-NNAL was the predominant isomer formed in all cytosolic incubations. In ten microsomal samples, NNAL was formed at an average rate of 3.8 +/- 1.6 pmol/mg/min; (R)-NNAL was the predominant isomer in this group. The average rate of NNAL formation in 18 other microsomal samples was significantly lower, 0.13 +/- 0.12 pmol/mg/min (p < 0.001); (S)-NNAL was the predominant isomer formed in this group.

CONCLUSION

In human pancreatic tissues, there is intraindividual variability regarding the capacity for, and stereoselectivity of, carbonyl reduction of NNK.

11Beta-hydroxysteroid dehydrogenase type 1: purification from human liver and characterization as carbonyl reductase of xenobiotics

11Beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes the interconversion of 11-oxo glucocorticoids to their 11-hydroxy metabolites, thereby controlling access of glucocorticoid hormones to the glucocorticoid receptor. Interestingly, evidence is emerging that 11beta-HSD1 fulfills an additional role in the metabolism of xenobiotic carbonyl compounds. In our studies, 11beta-HSD1 was identified as a microsomal reductase that initiates the final detoxification of xenobiotics by reducing them to alcohols that are easier to conjugate and eliminate. With its pluripotent substrate specificities for glucocorticoids and xenobiotics, 11beta-HSD1 adds to an expanding list of those hydroxysteroid dehydrogenases which, on the one hand, are capable of catalyzing the carbonyl reduction of non-steroidal carbonyl compounds, and which, on the other hand, exhibit great specificity to their physiological steroid substrates. It is conceivable that large interferences must occur between endogenous steroid metabolism and the detoxification of xenobiotic compounds on the level of hydroxysteroid dehydrogenases.

Glucocorticoid Metabolism in the Human Fetal Lung: Implications for Lung Development and the Pulmonary Surfactant System

It has been nearly 35 years since Liggins and Howie first reported the benefits of antenatal glucocorticoid (GC) treatment to promote the maturation of the human fetal lung, and nearly that long since Pasqualini and colleagues demonstrated that the human fetal lung actively metabolizes GCs. Since that time, our understanding of the effects of GCs on fetal lung maturation and pulmonary surfactant production has increased dramatically. Similarly, characterization of the enzymes involved in GC metabolism has greatly expanded our understanding of GC signaling in target tissues. In man, the biologically active GC (cortisol) and the biologically inactive GC (cortisone) are interconverted by the tissue-specific expression of the type 1 and type 2 11beta-hydroxysteroid dehydrogenase enzymes (HSD1 and HSD2). Much of the research on GC metabolism in peripheral target tissues has focused on the role of HSD1 in amplifying the effects of GCs in liver and adipose tissue or on the role of HSD2 in blocking the effects of GCs in the kidney and placenta. In contrast, the role of GC metabolism in modulating the effects of GCs on fetal lung maturation and the pulmonary surfactant system in humans is less understood. The goal of this review article is to present a brief overview of the role of GCs in human fetal lung maturation and pulmonary surfactant production, and to familiarize the reader with the biochemistry of the metabolism of natural and synthetic GCs by the HSD enzymes. In addition, we will review data concerning the expression and activity of the HSD enzymes in the human fetal lung and contrast this to what is known about the HSD enzymes in the fetal rodent lung. Although rodents, rabbits, sheep, and several primates have been invaluable model systems for the study of fetal lung development, we have chosen to largely focus this review on human lung, since there are significant differences in GC metabolism between humans and other species.

Melanocyte and keratinocyte carcinogenesis: p53 family protein activities and intersecting mRNA expression profiles

Melanocytes and keratinocytes were analyzed for potential roles of p53, p73, and p63 tumor suppressor family proteins and of malignancy-specific gene expression changes in the etiology of multi-step cancer. Melanocytes expressed deltaNp73alpha, two p63 isoforms and p53. Although p21 and Noxa mRNA levels increased following DNA damage, p53 family member binding to p21 and Noxa DNA probes was undetectable, suggesting p53 family-independent responses. In contrast, keratinocytes expressed multiple isoforms each of p73 and p63 that were induced to bind p21 and Noxa DNA probes after ionizing (IR) or after ultraviolet B (UVB) irradiation, correlating with p21 and Noxa mRNA induction and with apoptosis. Interestingly, IR-resistant malignant melanocytes and keratinocytes both exhibited Noxa mRNA induction after UVB treatment, correlating with DNA binding of p53 family proteins to the Noxa probe only in keratinocytes. To uncover other malignancy-specific events, we queried mouse initiated keratinocyte clones for early changes that were exacerbated in malignant derivatives and also differentially expressed in human advanced melanoma versus normal melanocytes. Using a new method for ranking and normalization of microarray data for 5000 probe sets, 27 upregulated and 13 downregulated genes satisfied our query. Of these, the majority was associated with late-stage human cancers and six were novel genes. Thus, clonal lineage mouse models representing early through late cancer progression stages may inform the focus on early, potentially causal events from microarray studies of human cancers, facilitating prognosis and molecular therapy.

Differentially expressed transcripts from phenotypically identified olfactory sensory neurons

In comparing purified mouse olfactory sensory neurons (OSNs) with neighboring cells, we identified 54 differentially expressed transcripts. One-third of the transcripts encode proteins with no known function, but the others have functions that correlate with challenges faced by OSNs. The OSNs expressed a diversity of signaling protein genes, including stomatin (Epb7.2), S100A5, Ddit3, Sirt2, CD81, Sdc2, Omp, and Ptpla. The elaboration of dendrites, cilia, and axons that places OSNs in contact with diverse cell types and signals presumably also requires large investments in cytoskeletal-associated proteins, lipid biosynthesis, and energy production. Several of the genes encode proteins that participate in these biological processes, including ATP5g3, Ndufa9, Sqrdl, Mdh1, Got1, beta-2 tubulin, Capza1, Bin3, Tom1, Acl6, and similar to O-MACS. Three transcripts had restricted expression patterns. Similar to O-MACS and Gstm2 had zonally restricted expression patterns in OSNs and sustentacular cells but not in Bowman's glands, suggesting that zonality can be differentially regulated by cell type. The mosaic expression pattern of S100A5 in approximately 70% of OSNs predicts that it is coexpressed with a subset of odorant receptors. We captured four abundant transcripts, Cyp2a4, similar to Cyp2g1, Gstm2, and Cbr2, that encode xenobiotic metabolizing enzymes expressed by sustentacular cells or Bowman's glands, reinforcing the interpretation that clearance of xenobiotic compounds is a major function of these cells. Within the olfactory epithelium, Cbr2 is a new anatomical marker for sustentacular cells. We also discovered that Reg3g is a marker for respiratory epithelium.

Significance of reductases in the detoxification of the tobacco-specific carcinogen NNK

Fewer than 20% of habitual smokers develop lung cancer, which suggests that genetic, environmental and nutritional factors contribute to the risk for developing this disease. Recently, five enzymes were shown to initiate the detoxification of nicotine-derived nitrosamine ketone (NNK), the most potent carcinogen present in tobacco. Importantly, four of these enzymes are potently inhibited by glycyrrhetinic acid, the main constituent of licorice. These observations might open novel and hitherto unexplored avenues for the risk assessment and prevention of tobacco-associated lung cancer.

Strain- and sex-related differences of carbonyl reductase activities in kidney microsomes and cytosol of rats

This study was designed to elucidate strain- and sex-related differences of carbonyl reductase activity in rat kidney by using the oral antidiabetic drug acetohexamide as substrate. The frequency distribution of carbonyl reductase activities in kidney microsomes of male Fischer 344 (Fischer), Sprague-Dawley, Wistar and Wistar-Imamichi (Wistar-IM) rats exhibited a marked strain-related difference. Furthermore, the enzyme activities in kidney microsomes of Fischer, Sprague-Dawley and Wistar rats were male-specific, resulting insignificant sex-related differences in these strains. There was no sex-related difference of carbonyl reductase activity in kidney microsomes of the Wistar-IM strain, which lacked its activity in both sexes. On the other hand, although carbonyl reductase activities were fully detectable in kidney cytosols from all the strains of male and female rats, no strain- or sex-related difference was observed among the cytosolic enzyme activities. These results provide new information for understanding the influence of internal factors on the renal metabolism of ketone-containing xenobiotics.

Inhaled glucocorticoids and adrenal function: an update

For the vast majority of asthmatic children, treatment with inhaled glucocorticoids is safe and effective. Mild impairment of adrenal function of doubtful clinical significance is known to occur in some children inhaling > or = 400 micro g/day budesonide and beclomethasone or > or = 200 micro g fluticasone. Recent reports of life-threatening adrenal failure in asthmatic children inhaling glucocorticoids, some of whom were prescribed licensed doses, have prompted the recommendation that the use of high-dose inhaled glucocorticoids, particularly fluticasone, should be avoided. However, the importance of correctly diagnosing asthma, of using the minimum dose of inhaled glucocorticoid required for symptom control and of regular growth-velocity assessment cannot be over-emphasised. Appropriate asthma management including the early introduction of steroid-sparing agents such as a long-acting beta-agonist or leukotriene antagonist may reduce the morbidity associated with inhaled glucocorticoid use but some children, for reasons as yet unknown, may exhibit increased sensitivity to the systemic effects of inhaled glucocorticoid treatment. Possible explanations for this, with reference to the pharmacology and molecular mechanisms of glucocorticoid action, are accompanied in this review by a summary of the recent case reports and discussion of assessment of adrenal function.

11Beta-hydroxysteroid dehydrogenase 1 expression in squamous cell carcinomas of the head and neck

11Beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) has been identified as a major detoxification enzyme of one of the most potent tobacco smoke-derived carcinogens, NNK. If not metabolized by 11beta-HSD1, activation of NNK by cytochrome p450 mono-oxidase 2D6 (CYP2D6) results in an electrophile intermediate responsible for DNA damage. Interindividual variability in the expression of 11beta-HSD1 and CYP2D6 has been found to influence the susceptibility to lung cancer. The aim of this study was to compare 11beta-HSD1 mRNA expression and CYP2D6 metabolizer status in pharyngeal tissues of patients with oropharyngeal carcinoma and controls. In 20 patients with oropharyngeal cancer and 15 non-smoking controls, the 11beta-HSD1 mRNA expression was assessed with RT-PCR. The frequency of genetic polymorphisms of the CYP2D6 gene was assessed using RFLP. It was found that 11beta-HSD1 mRNA is expressed in human pharyngeal mucosa. It is upregulated in mucosa exposed to tobacco smoke. In tumour tissues, 11beta-HSD1 expression was significantly lower than in non-affected mucosa. The frequency distribution of CYP2D6 gene polymorphisms was similar in patients and controls. Chronic tobacco abuse results in 11beta-HSD1 enzyme induction. A reduction of 11beta-HSD1 expression in tumour tissues could be a consequence of malignantly transformed cells. It remains unclear if the lower 11beta-HSD1 expression gives rise to an increased rate of additional mutations.

Clinical relevance of airway 11beta-hydroxysteroid dehydrogenase type II enzyme in asthma

11beta-hydroxysteroid dehydrogenases (11beta-HSD) are responsible for the conversion of bioactive glucocorticoids to and from inactive metabolites. 11beta-HSD2 is generally considered a high-affinity inactivator of natural glucocorticoids, although its activity with synthetic compounds in vivo is unknown. Inhaled corticosteroids (ICS) remain the primary antiinflammatory agents for treating asthma, but little is known about their metabolism in the lung. The aims of this study were to determine whether the 11beta-HSD2 enzyme can be localized to human airway tissue and whether differential expression of this enzyme relates to asthma severity and ICS needs. We studied airway biopsy specimens from 22 asthmatic subjects, in two groups: (1) a group not treated with ICS (n = 7); and (2) a group treated with ICS (range: 200 to 1,500 microg/d; n = 15). A control population consisted of nine nonasthmatic subjects. Immunostaining was done with an immunopurified antibody to human 11beta-HSD2. Immunoreactivity was generally localized to the endothelium of vessels in the lamina propria and to airway epithelium both in asthmatic patients and nonasthmatic controls. There was a statistically significant inverse relationship between the ICS dose required for effective treatment and the extent of epithelial 11beta-HSD2 staining (r = -0.44; p = 0.04). This is consistent with 11beta-HSD2 acting as an oxidoreductase that regenerates rather than inactivates ICS. This study suggests that glucocorticoid sensitivity in the lung is not determined by ICS breakdown, but may be related to 11beta-HSD2 sustaining the activation of synthetic glucocorticoids.

Effects of vitamins and common drugs on reduction of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in rat microsomes

4-(Methylnitrosamino)-1-(3-pyridyl)-butanone (NNK) is a tobacco-specific nitrosamino that requires metabolic activation by cytochrome P450 enzymes. The activation of NNK by cytochrome P450 enzymes leads to the formation of different metabolites. Detoxification of NNK usually occurs via carbonyl reduction to its hydroxyl product, 4-(methylnitrosamino)-1-(3-pyridyl)-butanol (NNAL). In the present study, the influences of common vitamins and P450 modulators on the reduction of NNK by rat microsomes were studied. The formation of NNAL but not other metabolites was detected by the described HPLC method. Among the vitamins tested, vitamins E, A (retinol), B6 and B5 were found to be marginal effective upon reduction of NNK while vitamins A (cis-acid), A (trans-acid), D2, D3, K1, K3, B1 and A (crocetin) increased the formation of NNAL from 3 to 21%. The effect of vitamin C-palmitate (<10 microM) was most pronounced followed by crocetin upon reduction of NNK. Clonidine, tolbutamide and atropine slightly increased the reduction of NNK while cimetidine showed no effects. The modulation of NNK reduction could reduce the carcinogenic potential of NNK, since the main detoxification pathway of NNK involves carbonyl reduction.

Light and electron microscopy localization of the 11beta-hydroxysteroid dehydrogenase type I enzyme in the rat

The 11beta-hydroxysteroid dehydrogenase type I enzyme (11betaHSD1) converts cortisone to cortisol in humans, and 11-dehydrocorticosterone to corticosterone in rodents. In the present study we used a new immunopurified polyclonal antibody, RAH113, to localize 11betaHSD1 at the light and electron microscopy levels in a wide range of rat tissues. 11betaHSD1 staining in the liver was of highest intensity around the central vein and decreased radially. In the lung, 11betaHSD1 was found at highest levels in the interstitial fibroblast, with levels in the type II pneumocyte an order of magnitude lower. RAH113 stained proximal tubules of the renal cortex and interstitial cells of the medulla and papilla. Adrenal 11betaHSD1 was confined to the glomerulosa and medulla, whereas the glucocorticoid-inactivating hydroxysteroid dehydrogenase isoform 11betaHSD2 was present in fascilulata/reticularis. 11betaHSD1 was found in parietal cells of the fundic region of the stomach, but not in the antrum. In the heart, 11betaHSD1 was detected in cells resembling interstitial fibroblasts of the endocardium and in the adventitial fibroblasts of blood vessels. Western blot analysis confirmed the presence of an antigen of the correct size (34 kDa) and intensity consistent with levels of enzyme activity previously reported in these tissues. Brain and testis also displayed the 34-kDa protein, confirming the expression of authentic 11betaHSD1 in these tissues. Electron microscopy of lung and kidney interstitial cells showed that 11betaHSD1 was localized both to the endoplasmic reticulum and the nuclear membrane. These results show that 11betaHSD1 is present in discrete cell populations where it may facilitate intracrine and paracrine glucocorticoid action in addition to its classical role of maintaining circulating glucocorticoids via activity in the liver.

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.

Carbonyl reductase

Carbonyl reductase (secondary-alcohol:NADP(+) oxidoreductase, EC 1.1. 1.184) belongs to the family of short chain dehydrogenases/reductases (SDR). Carbonyl reductases (CBRs) are NADPH-dependent, mostly monomeric, cytosolic enzymes with broad substrate specificity for many endogenous and xenobiotic carbonyl compounds. They catalyze the reduction of endogenous prostaglandins, steroids, and other aliphatic aldehydes and ketones. They also reduce a wide variety of xenobiotic quinones derived from polycyclic aromatic hydrocarbons. CBR reduces the anthracycline anticancer drugs, daunorubicin(dn) and doxorubicin (dox) to their C-13 hydroxy metabolites, changing the pharmacological properties of these drugs. Emerging data on CBRs over the last several years is generating new insights on the potential involvement of CBRs in a variety of cellular and molecular reactions associated with drug metabolism, detoxication, drug resistance, mutagenesis, and carcinogenesis.

Human 11beta-hydroxysteroid dehydrogenase 1/carbonyl reductase: recombinant expression in the yeast Pichia pastoris and Escherichia coli

Detoxification of aldehydes and ketones generally proceeds via reduction to their corresponding alcohols, which are then conjugated and eliminated. We focused our interest on 11beta-hydroxysteroid-dehydrogenase type 1 (11beta-HSD 1), a pluripotent enzyme which physiologically performs the interconversion of active and inactive glucocorticoid hormones, and which also participates in xenobiotic carbonyl compound detoxification. 11beta-HSD 1 belongs to the protein superfamily of the short-chain dehydrogenases/reductases (SDR), and has been structurally and functionally characterized. 11beta-HSD 1 is a glycosylated membrane protein which is very difficult to purify in an active state. In addition, expression levels in humans differ in a wide range. In order to facilitate biochemical and molecular studies on the significance of human 11beta-HSD 1 in detoxification processes, we have successfully performed the overexpression of recombinant human 11beta-HSD 1 in the yeast Pichia pastoris and in Escherichia coli. Recombinant 11beta-HSD 1 from E. coli was purified to homogeneity and used to generate a polyclonal antibody. The enzyme had no enzymatic activity, possibly due to the lack of glycosylation and/or incorrect folding in E. coli. In contrast, 11beta-HSD 1 overexpressed in P. pastoris was enzymatically active towards its physiological glucocorticoid substrates as well as towards xenobiotic carbonyl compounds. In western blot experiments the antibody crossreacted with both recombinant 11beta-HSD 1 forms and with the native enzyme from mouse and human liver. In conclusion, recombinant 11beta-HSD 1 from P. pastoris serves as a valuable tool for future studies on carbonyl compound detoxification.

Expression of proopiomelanocortin, corticotropin-releasing hormone (CRH), and CRH receptor in melanoma cells, nevus cells, and normal human melanocytes

Proopiomelanocortin (POMC) is a 31 kDa prohormone that is processed to various bioactive peptides, including adrenocorticotropin (ACTH), melanotropins (alpha, beta, gamma-MSH), lipotropins, and endorphins. POMC is expressed not only in the pituitary gland but also in a variety of nonpituitary organs and tumors, including melanomas. We previously showed that normal human melanocytes produce and secrete alpha-MSH and ACTH, and furthermore, that advanced melanoma cells generally produce higher amounts of POMC peptides that correlate with tumor progression. To elucidate the mechanism of this upregulation, the expression of genes encoding corticotropin-releasing hormone (CRH) and its receptor, CRH-R, as well as POMC and the MSH receptor (MC1-R), was evaluated by reverse transcriptase-polymerase chain reaction using cultured human melanoma cells, nevus cells, and normal melanocytes. Our results show that all melanocytic cells express CRH, CRH-R, POMC, and MC1-R, with highest intensities in melanoma cells. Furthermore, immunohistochemistry shows that CRH as well as POMC is strongly expressed in advanced melanomas, such as vertically growing lesions of acral lentiginous, nodular and metastatic melanomas, in contrast to negative expression in nevus cells. These results indicate that tumor progression accentuates CRH, CRH-R, and POMC expression by melanoma cells.