Amino acid substitution R384P in aldosterone synthase causes corticosterone methyloxidase type I deficiency.

Corticosterone methyloxidase type I (CMO-I) deficiency is an autosomal recessively inherited disorder causing congenital hypoaldosteronism due to defects in aldosterone synthase (P450aldo), the enzyme that converts 11-deoxycorticosterone to corticosterone, 18-hydroxycorticosterone, and aldosterone. To clarify the molecular basis of CMO-I deficiency and gain further insight into the structure-function relationship of P450aldo, we cloned and sequenced the CYP11B2 gene (encoding P450aldo) of a male Caucasian patient suffering from CMO-I deficiency and identified a single point mutation leading to substitution of the highly conserved arginine-384 by proline (R384P). Differential hybridization of mutation-specific oligonucleotide probes to polymerase chain reaction-amplified CYP11B2 fragments revealed that both parents were heterozygous carriers for R384P, whereas the patient appeared homozygous. The patient's healthy brother and 85 individuals without known aldosterone synthase deficiency did not carry the R384P mutation. Introduction of this mutation into a CYP11B2 complementary DNA expression vector construct and subsequent expression in COS cells revealed that R384P leads to complete loss of 11 beta- and 18-hydroxylase activities of P450aldo. Thus, the R384P mutation provides a molecular explanation for the CMO-I deficiency in this patient and suggests that arginine-384 plays a major role in P450aldo function.

Cloning and stable expression of the human mitochondrial cytochrome P45011B1 cDNA in V79 Chinese hamster cells and their application for testing of potential inhibitors.

V79 Chinese hamster cells are being genetically engineered to express human mitochondrial cytochromes P450 as an analytical tool for studying adrenal steroid synthesis. Here, a V79 derived cell line is presented expressing the enzymatically active human cytochrome P45011B1 (CYP11B1) in a stable and constitutive manner. Full length CYP11B1 cDNA was obtained from surgically removed normal adrenal gland by polymerase chain reaction. The cDNA was recombined with a SV40 early promoter containing plasmid for stable integration and expression in V79 cells upon gene transfer. The presence of the human CYP11B1 cDNA in the genome of the transfected cells was confirmed by Southern analysis. CYP11B1 cDNA directed expression was detected by Northern analysis. CYP11B1 dependent hydroxylation of deoxycorticosterone and 11-deoxycortisol was measured by HPLC analysis. Interestingly, the nonsteroidogenic lung fibroblast derived V79 Chinese hamster cell line was able to support human CYP11B1 mediated steroid hydroxylation without simultaneous heterologous expression of the human electron transfer system, adrenodoxin, and adrenodoxin reductase. CYP11B1 inhibitory potency of metyrapone, spironolactone, and the azole derivatives ketoconazole, clotrimazole, miconazole, and fluconazole was measured using the newly established V79MZh11B1 cell line. Thus, beside steroid metabolism studies in general, this cell line may also serve as an in vitro tool for monitoring the interference of drugs with 11 beta-hydroxylase activity.

Differential regulation of 11 beta-hydroxylase and aldosterone synthase in human adrenocortical H295R cells.

In humans the last steps in the synthesis of aldosterone and cortisol rely on the activity of two cytochrome P450 genes termed CYP11B2 (aldosterone synthase; P450aldo) and CYP11B1 (11 beta hydroxylase; P450cl1). The mechanisms which lead to differential expression of these two genes within the adrenal cortex are not well-defined. The human adrenocortical cell line. H295R, was utilized in this study to examine the intracellular second messenger pathways regulating expression of P450aldo and P450c11. using specific ribonuclease protection assays. Treatment of H295R cells with angiotensin II or potassium (K+) caused a time-dependent induction in the level of P450aldo transcripts. While K+ treatment was more specific for the induction of P450aldo mRNA, treatment with angiotensin II increased levels of both P450aldo and P450c11 transcripts. To define the second messenger systems which influence transcript levels for these enzymes, the effects of agonists of the protein kinase A, protein kinase C, and calcium pathways were tested on the expression of P450aldo and P450c11. Activation of the protein kinase A pathway by the agonists, dibutyryl cAMP or forskolin, preferentially increased the P450c11 transcript to a greater degree than P450aldo. Interestingly, activation of the protein kinase C pathway by tetradecanoylphorbol acetate (TPA) did not alter transcripts for either P450aldo or P450c11. The calcium channel agonist BAYK 8644 mimicked the effects of K+ by increasing the transcript for P450aldo. However, the calcium channel blocker nifedipine attenuated the stimulatory effects of angiotensin II and K+ on the levels of P450aldo. However, the calcium channel blocker nifedipine attenuated the stimulatory effects of angiotensin II and K+ on the levels of P450aldo transcripts without affecting the stimulatory effect of dbcAMP. This study demonstrates that the protein kinase A pathway preferentially induces P450c11 mRNA over that of P450aldo. In addition, pharmacologic agents that affect calcium levels provide evidence for an additional regulatory mechanism in modulating the expression of P450aldo. This is of importance since the major physiologic regulators of aldosterone secretion, angiotensin II and K+ are able to increase intracellular calcium but have little effect on intracellular cAMP levels.

Demineralized Bone Matrix-stimulated Bone Regeneration in Rats Enhanced by an Angiogenic Dipeptide Derivate.

A lysyl-proline derivate (LP) known to stimulate angiogenesis and formation of granulation tissue was tested as a local additive to allogeneic demineralized bone matrix (DBM) using a rat craniotomy model. Peracetic-acid sterilized DBM (10 mg/defect) was implanted into three groups of 45 animals each with 0, 6 and 20 microg LP. Subsequent evaluation was done by descriptive histology, histomorphometry, and determination of the calcium content of the explants 7, 14, 28, 42 and 84 days post-implantation. Grafting with DBM alone resulted in defect bridging by newly formed bone with incorporated DBM residues on day 84. Addition of LP to the implants caused an enhanced capillarization on day 14 and 28 as well as an enhanced mineralization on day 14, 28, 42 and 84. Both effects were dose-dependent. These data suggest that the local application of a synthetic angiogenic factor significantly improve bone regeneration in DBM-grafted trephine defects in rats. Thereby, they reinforce the opinion that early angiogenesis is crucial for a number of subsequent events in the bone regeneration process.

Carrier-mediated residual K+ and Na+ transport of human red blood cells.

Residual, i.e., (ouabain, bumetanide, and EGTA)-insensitive K+ and Na+ influxes as well as effluxes of human red blood cells are enhanced in isotonic solutions of low (NaCl + KCl) concentration using sucrose to maintain constant osmolarity. Various carrier models were tested to fit the experimental data of these fluxes simultaneously. The residual K+ and Na+ fluxes can be described on the basis of a carrier mechanism of competing substrates with modifier sites.

Cloning of CYP11B1 and CYP11B2 from normal human adrenal and their functional expression in COS-7 and V79 Chinese hamster cells.

The cDNAs of human 11 beta hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) were cloned from surgically removed normal human adrenal using polymerase chain reaction. The cloned cDNAs were transfected into COS-7 cells and steroid hydroxylase activity of the two cytochromes P450 expressed was determined in order to elucidate their the functional characteristics. Stable expression of human CYP11B1 or CYP11B2 was performed in V79 hamster cells and confirmed by Southern blotting, Northern blotting, and enzymatic activity. Interestingly, recombinant V79 cells were able to support CYP11B1 and CYP11B2 dependent steroid conversion without additional heterologous expression of the corresponding electron donor system.

Conferring aldosterone synthesis to human CYP11B1 by replacing key amino acid residues with CYP11B2-specific ones.

Performing residue-swapping experiments between the highly conserved human steroidogenic proteins CYP11B1 and CYP11B2 we recently demonstrated that replacement of specific residues at position 301, 302 and 320 in the aldosterone-producing CYP11B2 protein for such residues that were specific for the highly similar cortisol-producing CYP11B1 protein elevated the 11beta-hydroxylase activity dramatically. Conversely, aldosterone synthesis in the triple mutant was severely impaired. Here we provide evidence that in a reciprocal experiment, CYP11B2-specific amino acids at position 320 and 335 endowed CYP11B1 with an 18-oxidase function amounting to 20% of the CYP11B2 wild-type activity, thus changing the specificity of steroid hydroxylation by only one point mutation. Combining substitutions at positions 296, 301, 302, 320, 335 and 339 did, however, not result in further enhancement. Paradoxically, 11beta-hydroxylation was not or only marginally affected in CYP11B1 mutants, indicating an alternative structural basis for this activity in CYP11B1 compared with the engineered CYP11B2 variant. Our results suggest that the sequence spanned by amino acids 301 and 335 constitutes part of the substrate-binding site in CYP11B1 and CYP11B2 as well. By constructing chimeric proteins we further investigated the effect of the C-terminal portions of both proteins and found that diverging residues at positions 471, 472, 492, 493 and 494 were insignificant for the stereospecificity and regiospecificity of steroid hydroxylation.

[Clinical study on the application of demineralized bone matrix (DBM) in surgical orthodontics]. / Klinische Studie zum Einsatz von demineralisierter Knochenmatrix (DBM) in der Chirurgischen Stomatologie.

Demineralized bone matrix has been tested in a clinical study concerning the filling of bone defects in the surgical stomatology. It is reported on the clinical results and the X-ray evaluation of the replacement of bones by demineralized bone matrix. Fifty two implantations in the maxilla and mandible of 51 patients were carried out to be able to evaluate the efficacy of demineralized bone matrix.

[Animal experiment research on the application of a human bone collagen substance]. / Tierexperimentelle Untersuchungen zum Einsatz einer Human-Knochen-Kollagen-Substanz.

The possibility of the application demineralised human cortical substance with a particle size of 315 micron was investigated on the filling of artificial defects at the tibial diaphysis in rabbit. A clear induction of the bone healing was observed histologically on the transplant side already after 4 weeks and the absence of a periosseous callus formation radiologically.

Human adrenal CYP11B1: localization by in situ-hybridization and functional expression in cell cultures.

CYP11B1 was detected in the human adrenal cortex and in human adenomas by in situ-hybridization methods. Specific riboprobes were generated and hybridized to sections of an Aldosterone Producing Adenoma (APA), the non-tumour portion of the corresponding adrenal gland and two adenomas not related to hyperaldosteronism. P45011B1 mRNA was clearly localized in the zona fasciculata/reticularis. Semi-quantitative analysis has been performed and seems to be applicable for a further classification of adrenal tumours. Stable expression of CYP11B1 cDNA was performed in V79 cells. The interference of different substances (metyrapone, spironolactone and different imidazole derivatives) with CYP11B1 activity was studied using this cell line. The cell line revealed to be suitable for analysis of the active site of CYP11B1 as well as for analysis of side effects of drugs on steroidogenesis.

[A method for the preparation of demineralized bone matrix]. / Verfahren zur Präparation demineralisierter Knochenmatrix.

A procedure for preparation of a demineralized bone matrix (DBM) implant is demonstrated. The main steps of this method are refrigeration, milling/sieving, defatting, demineralization, freeze-drying and sterilization. These steps are standardized but also viable. Therefore this method is on the one hand international comparable on the other hand it creates the possibility for further investigations to improve the osteoinductive capacity of DBM.

[Relevant laboratory diagnostic methods for the evaluation of the osteoinductivity of bone matrix implants]. / Relevanz labordiagnostischer Methoden zur Bewertung der Osteoinduktivität von Knochenmatriximplantaten.

For the valuation of the osteoinductive efficacy of different bone grafts bears upon increasing the determination of the alkaline phosphatase, the content of calcium, hydroxyproline and protein. We could prove the quantitative differentiation of different prepared bone matrix implants being possible, nevertheless the histological examination is an unavoidable, full of good sense completion.

Site-selective dephosphorylation of the platelet-derived growth factor beta-receptor by the receptor-like protein-tyrosine phosphatase DEP-1.

Ligand stimulation of PDGF beta-receptors leads to autophosphorylation of the regulatory tyrosine 857 and of tyrosine residues that in their phosphorylated form serve as docking sites for Src homology 2 domain-containing proteins. Regulation of the PDGF beta-receptor by protein-tyrosine phosphatases is poorly understood. We have investigated PDGF beta-receptor dephosphorylation by receptor-like protein-tyrosine phosphatase DEP-1 using a cell line with inducible DEP-1 expression and by characterizing in vitro dephosphorylation of the PDGF beta-receptor and of receptor-derived phosphopeptides by DEP-1. After DEP-1 induction PDGF beta-receptor.DEP-1 complexes and reduced receptor tyrosine phosphorylation were observed. Phosphopeptide analysis of the PDGF beta-receptors from DEP-1-expressing cells and of the receptors dephosphorylated in vitro by DEP-1 demonstrated that dephosphorylation of autophosphorylation sites of the receptor differed and revealed that the regulatory Tyr(P)(857) was not a preferred site for DEP-1 dephosphorylation. When dephosphorylation of synthetic receptor-derived peptides was analyzed, the selectivity was reproduced, indicating that amino acid sequence surrounding the phosphorylation sites is the major determinant of selectivity. This notion is supported by the observation that the poorly dephosphorylated Tyr(P)(562) and Tyr(P)(857), in contrast to other analyzed phosphorylation sites, are surrounded by basic amino acid residues at positions -4 and +3 relative to the tyrosine residue. Our study demonstrates that DEP-1 dephosphorylation of the PDGF beta-receptor is site-selective and may lead to modulation, rather than general attenuation, of signaling.

Functional characterization of atherosclerosis-associated Ser128Arg and Leu554Phe E-selectin mutations.

The cellular adhesion molecule E-selectin is expressed on activated endothelial cells, and is involved in the process of adherence of blood cells to vessel endothelium in inflammatory events such as atherosclerosis. In a recent study we found a Ser128Arg mutation in the EGF domain as well as a Leu554Phe mutation in the membrane domain of E-selectin. We also established increased frequencies of both mutations among young patients with severe coronary atherosclerosis. In the present study we investigated the influence of these mutations on cell adhesion and on the release of soluble E-selectin. Mutants were created by site-directed mutagenesis and COS cells were transfected with E-selectin, either wild-type or mutant. Antibody-binding studies and cell-adhesion assays were performed on transfected COS cells and on interleukin-1 beta-stimulated HUVECs. Soluble E-selectin in supernatants of wild type and Leu554Phe mutant-transfected COS cells was measured by ELISA. We discovered significant differences in the strength of HL-60 cell adhesion for the Ser128Arg mutant: in comparison with the wild type, the strength of adhesion to the mutant was reduced on transfected COS cells (P < 0.01) as well as on stimulated HUVECs (P < 0.01). Significantly diminished release of soluble E-selectin was detected for the Leu554Phe membrane domain mutant, in comparison with the wild type. In summary, the mutations studied here influence the E-selectin function in vitro and may be considered as one of the risk factors involved in the complex pathogenesis of atherosclerosis.