Human type 10 17 beta-hydroxysteroid dehydrogenase: molecular modelling and substrate docking

17 beta-hydroxysteroid dehydrogenases catalyze the oxidoreduction of hydroxy/oxo groups at position C17 of steroid hormones, thereby constituting a prereceptor control mechanism of hormone action. At present, 11 different mammalian 17 beta-hydroxysteroid dehydrogenases have been identified, catalyzing the cell- and steroid-specific activation and inactivation of estrogens and androgens. The human type 10 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD-10) is a multifunctional mitochondrial enzyme that efficiently catalyzes the oxidative inactivation at C17 of androgens and estrogens. However, it also mediates oxidation of 3 alpha-hydroxy groups of androgens, thereby reactivating androgen metabolites. Finally, it is involved in beta-oxidation of fatty acids by catalyzing the L-hydroxyacyl CoA dehydrogenase reaction of the beta-oxidation cycle. These features and expression profiles suggest a critical role of 17 beta-HSD-10 in neurodegenerative and steroid-dependent cancer forms. Since no three-dimensional structure of 17 beta-HSD-10 is available, homology modelling was carried out to understand the molecular basis of these substrate specificities. The structure obtained displays the properties of a one-domain, alpha/beta fold enzyme of the SDR family. The active site is located within a large, hydrophobic cleft, which forms optimal contacts with the different steroid surfaces. The data provide explanations for the substrate specificities toward the various classes of sex steroid hormones. The model is suitable to explore substrate and inhibitor characteristics that may be used in the development of novel strategies in the treatment of degenerative or malignant diseases.

Biochemical defects in 11-cis-retinol dehydrogenase mutants associated with fundus albipunctatus

Mutations in the gene encoding 11-cis-retinol dehydrogenase (RDH5; EC ) are associated with fundus albipunctatus, an autosomal recessive eye disease characterized by stationary night blindness and accumulation of white spots in the retina. In addition, some mutated alleles are associated with development of cone dystrophy, especially in elderly patients. The numbers of identified RDH5 mutations linked to fundus albipunctatus have increased considerably during recent years. In this work, we have characterized the biochemical and cell biological properties of 11 mutants of RDH5 to understand the molecular pathology of the disease. All RDH5 mutants showed decreased protein stability and subcellular mislocalization and, in most cases, loss of enzymatic activity in vitro and in vivo. Surprisingly, mutant A294P displays significant enzymatic activity. Cross-linking studies and molecular modeling showed that RDH5 is dimeric, and co-expression analyses of wild-type and mutated alleles showed that the mutated enzymes, in a trans-dominant-negative manner, influenced the in vivo enzymatic properties of functional variants of the enzyme, particularly the A294P mutant. Thus, under certain conditions, nonfunctional alleles act in a dominant-negative way on functional but relatively unstable mutated alleles. However, in heterozygous individuals carrying one wild-type allele, the disease is recessive, probably due to the stability of the wild-type enzyme.

Nonrandom karyotypic features in basal cell carcinomas of the skin

Cytogenetic analysis of short-term cultured 44 basal cell carcinomas (BCC) revealed clonal karyotypic abnormalities in 38 tumors. Relatively complex karyotypes (at least four structural and/or numerical changes per clone) with unbalanced structural as well as numerical aberrations were found in eight (approximately 21%) of the BCC, while the remaining BCC (79%) had simple karyotypes (1 to 3 aberrations per clone). Numerical changes only were found in 16 tumors, 15 BCC displayed both numerical and structural aberrations, and the remaining 7 BCC showed only structural aberrations. Extensive intratumoral heterogeneity, in the form of cytogenetically unrelated clones, was found in 21 tumors, whereas related subclones were present in 10 tumors. In order to obtain an overall karyotypic picture in BCC, the findings of our previously published 25 BCC have been reviewed. Our combined data indicate that BCC are characterized by nonrandom karyotypic patterns. A large subset of BCC is characterized by nonrandom numerical changes, notably, +18, +X, +7, and +9. Structural rearrangements often affect chromosomes 1, 4, 2, 3, 9, 7, 16, and 17. A number of chromosomal bands are frequently involved, including 9q22, 1p32, 1p22, 1q11, 1q21, 2q11, 4q21, 4q31, 1p36, 2q37, 3q13, 7q11, 11p15, 16p13, 16q24, 17q21, and 20q13. When the genomic imbalance is assessed, it has been shown that several chromosome segments are repeatedly involved in losses, namely loss of the distal part of 6q, 13q, 4q, 1q, 8q, and 9p. A correlation analysis between the karyotypic patterns and the clinico-histopathologic parameters has been undertaken in the 44 BCC of the present series. The cytogenetic patterns show a significant correlation with tumor status (P=.025), that is, that cytogenetically more complex tumors are also those clinically the most aggressive. Also, the frequency of cytogenetically unrelated clones is significantly higher in recurrent BCC than that in primary lesions (P=.05). No clear-cut association has been found between the karyotypic patterns and histologic subtypes or tumor sites.

Cadmium exposure and end-stage renal disease

Environmental exposure to cadmium may cause kidney damage and tubular proteinuria. We investigated the relationship between low-level cadmium exposure and end-stage renal disease (ESRD), indicated by renal replacement therapy (RRT), in a Swedish population environmentally or occupationally exposed to cadmium. Based on records of all persons in the population previously or presently employed in cadmium-battery production or residing in cadmium-polluted areas near the battery plants, we defined exposure as high (occupational), moderate (domicile < 2 km from a plant), low (domicile 2 to 10 km from a plant), or no exposure (domicile > 10 km from a plant). Comprehensive data were available for all individuals undergoing RRT since 1978. The annual incidence of RRT increased from 41 per million in the age group 20 to 29 years to 243 per million in the age group 70 to 79 years and was greater in a priori-defined populations with cadmium exposure. Adjusting for age and sex gave an increased Mantel-Haenszel rate ratio (MH-RR) of 1.8 (95% confidence interval [CI], 1.3 to 2.3) for RRT in the cadmium-exposed population compared with the unexposed group; the MH-RR was even higher for women (MH-RR, 2.3; 95% CI, 1.5 to 3.5). Directly age-standardized rate ratios for RRT and cadmium exposure increased from 1.4 (95% CI, 0.8 to 2.0) in the low-exposure group to 1.9 (95% CI, 1.3 to 2.5) and 2.3 (95% CI, 0.6 to 6.0) in the moderate- and high-exposure groups, respectively. We conclude that exposure to occupational or relatively low environmental levels of cadmium appears to be a determinant for the development of ESRD.

Determination of clenbuterol residues in bovine urine by optical immunobiosensor assay

Clenbuterol (CBL) is an orally active beta2-adrenoceptor agonist which has been used in veterinary medicine as a broncodilator and an agent of uterine relaxation. It has however become better known as a drug used illegally to promote growth in farm animals. A rapid and sensitive biosensor assay was developed to detect CBL residues in bovine urine. The method involved a simple extraction procedure using tert-butyl methyl ether followed by analysis on the biosensor with results obtained against a buffer calibration curve. The assay allowed up to 88 samples to be analyzed per working day, with each cycle on the biosensor taking approximately 7 min to complete. The limit of detection (LOD) was determined as 0.27 ng/mL using 20 EU reference blank urine samples. The intra-assay Sr ranged from 4.7-7.6% for 3 control samples while the interassay Sr ranged from 9.2-12.7%. The recovery was found to be approximately 95%. A series of incurred urine samples were assayed and the results compared by Enzyme immunoassay (EIA), radio-immunoassay (RIA), and gas chromatography/mass spectrometry (GC/MS) analysis. Urine samples taken from local abattoirs were also analyzed by the biosensor method and by EIA analysis. The antibody used in the biosensor test exhibited high cross reactivity with at least 7 other beta-agonists allowing detection of these compounds at less than 1 ng/mL in bovine urine.

Cloning of a novel growth hormone-regulated rat complementary deoxyribonucleic acid with homology to the human alpha1B-glycoprotein, characterizing a new protein family

A sex-specific secretion of GH prevails in the rat. This has bearings on the expression of target genes, particularly in the liver. We have used suppressive subtractive hybridization to search for genes expressed in response to the female-characteristic, near-continuous secretion of GH. One sequence was particularly abundant among the obtained clones. After isolation of the corresponding full-length complementary DNA using rapid amplification of complementary DNA ends, it was found to be homologous to the human alpha1B-glycoprotein. Sequence comparisons suggest that the human alpha1B-glycoprotein and the rat homolog are members of a new family of proteins, of which at least four additional forms were found in the databases of human and mouse expressed sequence tags. In situ hybridization confirmed the female-specific expression, and by RNase protection analysis a liver-specific expression was indicated. Up-regulation of the messenger RNA by continuous exposure to GH, but not to the male-characteristic intermittent exposure, was demonstrated in hypophysectomized rats and in cultured primary hepatocytes.

A case-referent study of cancer mortality among sulfate mill workers in Sweden

OBJECTIVES

To investigate whether workers in Swedish sulfate mills have an increased risk of death from certain malignancies that have previously been linked to the pulping process.

METHODS

Subjects of the study (n=2480) were men aged 40-75 at death during 1960-89 in the parishes surrounding four sulfate mills. Exposure assessment was based on information from the personnel files in the mills- 35% of the subjects were recognised there, and work categories were created.

RESULTS

Among all sulfate mill workers, the odds ratio (OR) (90% confidence interval (90% CI)) for death from lung cancer was 1.6 (1.1 to 2.3), pleural mesotheliomas 9.5 (1.9 to 48), brain tumours 2.6 (1.2 to 5.3), and liver or biliary tract cancer 2.3 (1.0 to 5.2). There was an increased mortality from leukaemia among workers in the soda recovery plant (5.9 (2.6 to 13)) and bleaching plant and digester house (2.8 (1.0 to 7.5)).

CONCLUSIONS

Sulfate mill workers were at increased risk of dying from lung cancer and pleural mesotheliomas, probably due to exposure to asbestos. Increased risks of brain tumours and cancers of the liver or biliary tract were also found but the aetiology is not obvious.

Prediction of amyloid fibril-forming proteins

In Alzheimer's disease and spongiform encephalopathies proteins transform from their native states into fibrils. We find that several amyloid-forming proteins harbor an alpha-helix in a polypeptide segment that should form a beta-strand according to secondary structure predictions. In 1324 nonredundant protein structures, 37 beta-strands with > or =7 residues were predicted in segments where the experimentally determined structures show helices. These discordances include the prion protein (helix 2, positions 179-191), the Alzheimer amyloid beta-peptide (Abeta, positions 16-23), and lung surfactant protein C (SP-C, positions 12-27). In addition, human coagulation factor XIII (positions 258-266), triacylglycerol lipase from Candida antarctica (positions 256-266), and d-alanyl-d-alanine transpeptidase from Streptomyces R61 (positions 92-106) contain a discordant helix. These proteins have not been reported to form fibrils but in this study were found to form fibrils in buffered saline at pH 7.4. By replacing valines in the discordant helical part of SP-C with leucines, an alpha-helix is found experimentally and by secondary structure predictions. This analogue does not form fibrils under conditions where SP-C forms abundant fibrils. Likewise, when Abeta residues 14-23 are removed or changed to a nondiscordant sequence, fibrils are no longer formed. We propose that alpha-helix/beta-strand-discordant stretches are associated with amyloid fibril formation.

Variations and constant patterns in eukaryotic MDR enzymes. Conclusions from novel structures and characterized genomes

Medium-chain dehydrogenases/reductases (MDR) alcohol dehydrogenases exhibit multiple forms through a number of gene duplications. A crucial duplication was the one leading from the glutathione-dependent formaldehyde dehydrogenase line to the liver alcohol dehydrogenase (ADH) lines of vertebrates, the first duplication of which can now be further positioned at early vertebrate times. Similarly, screening of MDR forms in recently completed eukaryotic genomes of Caenorhabditis elegans and Drosophila melanogaster suggest that the MDR family may constitute a moderately sized protein family centered around a limited number of enzyme activities of five different structural types.

Proximal colorectal dysplasia or cancer in ulcerative colitis. The impact of primary sclerosing cholangitis and sulfasalazine: results from a 20-year surveillance study

PURPOSE

Known risk factors for the development of colorectal dysplasia or cancer in ulcerative colitis are total colonic involvement and long duration of the disease. It has recently been suggested that presence of primary sclerosing cholangitis is another independent risk factor-especially for proximal colorectal dysplasia or cancer-and that treatment with sulfasalazine might reduce the frequency of colorectal cancer in ulcerative colitis; the present study was undertaken to shed light on the validity of these theories.

METHODS

A total of 143 patients with ulcerative colitis underwent regular colonoscopies and multiple biopsies in a 20-year surveillance program for studies of long-standing total ulcerative colitis. Fifty-one of the patients developed colorectal dysplasia or cancer. Patient records were scrutinized retrospectively for information of presence of primary sclerosing cholangitis, site of the colorectal malignancy, and results of sulfasalazine treatment.

RESULTS

Nineteen of the patients had primary sclerosing cholangitis; these ran a significantly higher risk of developing colorectal dysplasia or cancer than patients with ulcerative colitis only. All colorectal cancers (n = 3) and 75 percent of all colorectal dysplasias or cancers among patients with primary sclerosing cholangitis were located in the proximal part of the colon, whereas 36 percent were found in that same region among the patients with ulcerative colitis without primary sclerosing cholangitis (P = 0.02). Sulfasalazine treatment showed no significant protective effect on the development of colorectal dysplasia or cancer in patients with ulcerative colitis.

CONCLUSION

The risk evaluation, as assessed by multivariate analysis, shows that primary sclerosing cholangitis proves to be an additional and independent risk factor for the development of colorectal dysplasia or cancer in patients with ulcerative colitis-particularly in the proximal part of the colon. The findings do not support the theory that sulfasalazine treatment exerts a protective effect against colorectal dysplasia or cancer.

Consensus predictions of membrane protein topology

We have explored the possibility that consensus predictions of membrane protein topology might provide a means to estimate the reliability of a predicted topology. Using five current topology prediction methods and a test set of 60 Escherichia coli inner membrane proteins with experimentally determined topologies, we find that prediction performance varies strongly with the number of methods that agree, and that the topology of nearly half of all E. coli inner membrane proteins can be predicted with high reliability (>90% correct predictions) by a simple majority-vote approach.

The N-terminal domain of 5-lipoxygenase binds calcium and mediates calcium stimulation of enzyme activity

Human 5-lipoxygenase (5-LO) is a key enzyme in the conversion of arachidonic acid into leukotrienes and lipoxins, mediators and modulators of inflammation. In this study, we localized a stimulatory Ca(2+)-binding site to the N-terminal region of the enzyme. Thus, in a (45)Ca(2+) overlay assay, the N-terminal 128 amino acids of recombinant human 5-LO (fused to glutathione S-transferase) bound radioactive calcium to about the same extent as intact 5-LO. The glutathione S-transferase fusion protein of the C-terminal part of 5-LO (amino acids 120-673) showed much weaker binding. A model of a putative 5-LO N-terminal domain was calculated based on the structure of rabbit reticulocyte 15-LO. This model resembles beta-sandwich C2 domains of other Ca(2+)-binding proteins. Comparison of our model with the C2 domain of cytosolic phospholipase A(2) suggested a number of amino acids, located in the loops that connect the beta-strands, as potential Ca(2+) ligands. Indeed, mutations particularly in loop 2 (N43A, D44A, and E46A) led to decreased Ca(2+) binding and a requirement for higher Ca(2+) concentrations to stimulate enzyme activity. Our data indicate that an N-terminal beta-sandwich of 5-LO functions as a C2 domain in the calcium regulation of enzyme activity.

Influence of the initial management regimen and family social situation on glycemic control and medical care in children with type I diabetes mellitus

It is well known that social family factors are of importance in diabetes care, but it is not clear whether the initial management regimen can buffer these factors. In a prospective, randomized intervention study, 36 children with diabetes mellitus (type I) were followed, the aim being to study if a family psychosocial intervention at diagnosis could improve glycemic control and minimize hospital admissions. The control group was treated initially in a hospital ward, while the study group received problem-based learning and family-therapeutic and social support in an out-hospital training apartment. A number of family social variables were evaluated at the time of diagnosis and 6, 12 and 24 mo later. Family function was assessed using the self-estimated Family Climate Test at these same time-points. HbAlc values and information concerning in- and out-hospital visits to the pediatric clinic were collected for the 5-y period following diagnosis. We found no association between the offered management regimen and glycemic control or rate of readmission. In the study group only, both parents reported a significant improvement of the family climate. An increased risk for poor glycemic control was recorded in children living in one-parent families (p = 0.03) or in families where the father had a low level of education (p = 0.04). Younger age (p = 0.05), a single-parent family (p = 0.05) and poor glycemic control (p = 0.02) were associated with more days of rehospitalization. The rate of divorce in the whole group was at least as high as in the normal population but, surprisingly, maternal dysfunction was associated with lower HbAlc value. The conclusion is that even with an initial management regimen designed to offer a family-individual care regimen based on accurate estimation of the psychological and pedagogical needs, the social family background is a most important factor for the glycemic control and need for readmission.

Recognition of glutamic acid decarboxylase (GAD) by autoantibodies from different GAD antibody-positive phenotypes

Autoantibodies against the smaller isoform of glutamic acid decarboxylase (GAD) are markers for Type 1 diabetes. GAD65 autoantibody (GAD65Ab)-positive individuals in the general population are, however, mostly at low risk of developing Type 1 diabetes, suggesting that GAD65Ab phenotypes may be associated with different underlying pathogenic processes. The aim of this study was to test the hypothesis that Type 1 diabetes patients (n = 243; group I), GAD65Ab-positive healthy individuals (n = 28; group II), and healthy first-degree relatives of Type 1 diabetes patients (n = 41; group III) have antibody phenotypes that recognize different GAD65 epitopes. Sera from groups I-III were tested for their binding to GAD65 and GAD67, as well as six different GAD65/67 fusion proteins. Regardless of group, sera reactive to both GAD65 and GAD67 showed broader epitope reactivity than GAD65-specific sera. Furthermore, Type 1 diabetes patients showed a more restricted epitope binding than healthy individuals and first-degree relatives, demonstrating significantly less binding to the N-terminal part of GAD65 and to GAD67. Our analysis demonstrates that the N-terminal part is essential for full antibody binding to GAD65, in particular, to the middle epitope. It is suggested that Type 1 diabetes is associated with restricted GAD65Ab epitope specificity.

Low level exposure to cadmium and early kidney damage: the OSCAR study

OBJECTIVES

To study the dose-response relation between cadmium dose and renal tubular damage in a population of workers and people environmentally or occupationally exposed to low concentrations of cadmium.

METHODS

Early kidney damage in 1021 people, occupationally or environmentally exposed to cadmium, was assessed from cadmium in urine to estimate dose, and protein HC (alpha(1)-microglobulin) in urine to assess tubular proteinuria.

RESULTS

There was an age and sex adjusted correlation between cadmium in urine and urinary protein HC. The prevalence of tubular proteinuria ranged from 5% among unexposed people to 50% in the most exposed group. The corresponding prevalence odds ratio was 6.0 (95% confidence interval (95% CI) 1.6 to 22) for the highest exposure group, adjusted for age and sex. Multiple logistic regression analysis showed an increasing prevalence of tubular proteinuria with urinary cadmium as well as with age. After adjustment to the mean age of the study population (53 years), the results show an increased prevalence of 10% tubular proteinuria (taking into account a background prevalence of 5%) at a urinary cadmium concentration of 1.0 nmol/mmol creatinine.

CONCLUSION

Renal tubular damage due to exposure to cadmium develops at lower levels of cadmium body burden than previously anticipated.

Biosensor assay of sulfadiazine and sulfamethazine residues in pork

Biosensor-based immunochemical screening assays for the detection of sulfadiazine (SDZ) and sulfamethazine (SMT) in muscle extract from pigs were developed. Samples were extracted with aqueous buffer and then centrifuged. This simple and straightforward preparation allowed up to 40 samples to be processed and analysed in 1 d. The limits of detection for the assays were found to be 5.6 ng g-1 for SDZ and 7.4 ng g-1 for SMT. These figures were well below the European and US legal limits for sulfonamides (100 ng g-1). The precision (RSD) between runs was < 8% and the recovery was between 91 and 98%. The validation proved the assays to be accurate and the analysis of routine field samples showed good correlation with an established TLC screening procedure. No false negative or positive results were obtained with blank and spiked samples. The influence of cross-reacting metabolites on immunoassays was demonstrated by testing incurred tissue samples, collected from sulfonamide treated pigs after only a short withdrawal period. The quantitative results obtained by biosensor analysis were a combination of parent sulfonamide plus N4-acetyl metabolite while the HPLC method used for confirmatory analysis detected only the parent sulfonamide. This gave rise to some false positive results and highlighted the need to use real samples in evaluating any assay thoroughly. False negative results were not obtained.

Pharmacogenetics of the alcohol dehydrogenase system

Alcohol dehydrogenase (ADH) constitutes a complex enzyme system with different forms and extensive multiplicity. A combination of constant and variable properties regarding function, multiplicity and structure of ADH is highlighted for the human system and extended to ADH forms in general. Future perspectives suggest continued studies in specific directions for distinction of metabolic, regulatory and pharmacogenetic roles of ADH.