Topological similarities in TGF-beta 2, PDGF-BB and NGF define a superfamily of polypeptide growth factors

BACKGROUND

The development of functional diversity through gene duplication and subsequent divergent evolution can give rise to proteins that have little or no sequence similarity, but retain similar topologies.

RESULTS

The crystal structures of nerve growth factor, transforming growth factor-beta 2 and platelet-derived growth factor-BB show that all three are based on a cystine-knot plus beta-strands topology. There is very little sequence identity between the three proteins and the relationship between the structures had not been deduced from sequence comparisons. Each growth factor is usually active as a dimer; each exists as a dimer in the crystal, but the relative orientations of the protomers are different in each case.

CONCLUSION

The structural motif of disulphide bonds and hydrogen-bonded beta-strands unexpectedly found in these three growth factors acts as a stable framework for elaboration of loops of low sequence similarity that contain the specificity for receptor interaction.

Renin inhibition by substituted piperidines: a novel paradigm for the inhibition of monomeric aspartic proteinases?

BACKGROUND

The aspartic proteinase renin catalyses the first and rate-limiting step in the conversion of angiotensinogen to the hormone angiotensin II, and therefore plays an important physiological role in the regulation of blood pressure. Numerous potent peptidomimetic inhibitors of this important drug target have been developed, but none of these compounds have progressed past clinical phase II trials. Limited oral bioavailability or excessive production costs have prevented these inhibitors from becoming new antihypertensive drugs. We were interested in developing new nonpeptidomimetic renin inhibitors.

RESULTS

High-throughput screening of the Roche compound library identified a simple 3, 4-disubstituted piperidine lead compound. We determined the crystal structures of recombinant human renin complexed with two representatives of this new class. Binding of these substituted piperidine derivatives is accompanied by major induced-fit adaptations around the enzyme's active site.

CONCLUSIONS

The efficient optimisation of the piperidine inhibitors was facilitated by structural analysis of the renin active site in two renin-inhibitor complexes (some of the piperidine derivatives have picomolar affinities for renin). These structural changes provide the basis for a novel paradigm for inhibition of monomeric aspartic proteinases.

Calcium gradient-dependent and calcium gradient-independent phosphorylation of sarcoplasmic reticulum by orthophosphate. The role of magnesium

Phosphorylation of the calcium-transport ATPase of skeletal muscle sarcoplasmic reticulum by inorganic phosphate was investigated in the presence or absence of a calcium gradient. The maximum phosphoprotein formation in the presence of a calcium gradient at 20 degrees C and pH 7.0 is approximately 4 nmol/mg sarcoplasmic reticulum protein, but only between 2.4 and 2.8 nmol/mg protein in the absence of a calcium gradient, using Ionophore X-537 A or phospholipase-A-treated sarcoplasmic reticulum vesicles. Maximum phosphoprotein formation independent of calcium gradient at 20 degrees C and pH 6.2 is in the range of 3.6--4 nmol/mg protein. Half-maximum phosphoprotein formation dependent on calcium gradient was achieved with 0.1--0.2 mM free orthophosphate at 10 mM free magnesium or at 0.1--0.2 mM free magnesium at 10 mM free orthophosphate. Phosphoprotein formation independent of calcium gradient is in accordance with a model which assumes, firstly, the formation of a ternary complex of the ATPase protein with orthophosphate and magnesium (E . Pi . Mg) in equilibrium with the phosphoprotein (E-Pi . Mg) and, secondly, an interdependence of both ions in the formation of the ternary complex. The apparent equilibrium constant was 0.6 and the apparent dissociation constants KMg, KMg', KPi and KPi' were 8.8, 1.9, 7.2 and 1.5 mM respectively, assuming a total concentration of the phosphorylation site per enzyme of 7 nmol/mg protein.

Differential Expression of Nitric Oxide Synthases in Bacterial Meningitis: Role of the Inducible Isoform for Blood‐Brain Barrier Breakdown

The aim of the study was to determine the differential expression of nitric oxide (NO) synthase (NOS) isoforms and the pathophysiologic relevance of inducible NOS (iNOS) in experimental pneumococcal meningitis. By use of reverse transcription-polymerase chain reaction analysis, immunohistochemistry, and Western blotting, increased brain mRNA and increased protein levels of endothelial NOS (eNOS) and iNOS were detected 24 h after intracisternal pneumococcal inoculation. In iNOS-deficient mice, disruption of the blood-brain barrier (BBB) was significantly reduced, compared with that in wild-type mice. This beneficial effect of iNOS deficiency was associated with a lack of nitrotyrosine immunoreactivity. Furthermore, brain protein levels of interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha and brain mRNA levels of macrophage inflammatory protein (MIP)-1alpha and MIP-2 were significantly reduced in infected animals lacking iNOS. These findings suggest that (1) not only iNOS but also eNOS is up-regulated in the acute phase of experimental bacterial meningitis, and (2) iNOS-derived NO contributes to peroxynitrite formation and BBB breaching in this disease.

Amino acid substitution (Ile194----Thr) in exon 5 of the lipoprotein lipase gene causes lipoprotein lipase deficiency in three unrelated probands. Support for a multicentric origin

Studies on the molecular biology of lipoprotein lipase (LPL) deficiency have been facilitated by the availability of LPL gene probes and the recent characterization of gene mutations underlying human LPL deficiency. Typically, missense mutations have predominated and show a preferential localization to exons 4 and 5. This distribution supports earlier studies attributing functional significance to residues encoded by these exons. We now report a further missense mutation within exon 5 of the LPL gene in three unrelated patients. Amplification of individual exons by the polymerase chain reaction and direct sequencing revealed a T----C transition at codon 194 of the LPL cDNA which results in a substitution of threonine for isoleucine at this residue. The catalytic abnormality induced by this mutation was confirmed through in vitro mutagenesis studies in COS-1 cells. Transfection with a LPL cDNA containing the codon 194 transition resulted in the synthesis and secretion of a catalytically defective protein. The Thr194 substitution was associated with two different DNA haplotypes, consistent with a multicentric origin for this mutation.

Structure-based design of beta-lactamase inhibitors. 1. Synthesis and evaluation of bridged monobactams

Bridged monobactams are novel, potent, mechanism-based inhibitors of class C beta-lactamases, designed using X-ray crystal structures of the enzymes. They stabilize the acyl-enzyme intermediate by blocking access of water to the enzyme-inhibitor ester bond. Bridged monobactams are selective class C beta-lactamase inhibitors, with half-inhibition constants as low as 10 nM, and are less effective against class A and class B enzymes (half-inhibition constants > 100 microM) because of the different hydrolysis mechanisms in these classes of beta-lactamases. The stability of the acyl-enzyme complexes formed with class C beta-lactamases (half-lives up to 2 days were observed) enabled determination of their crystal structures. The conformation of the inhibitor moiety was close to that predicted by molecular modeling, confirming a simple reaction mechanism, unlike those of known beta-lactamase inhibitors such as clavulanic acid and penam sulfones, which involve secondary rearrangements. Synergy between the bridged monobactams and beta-lactamase-labile antibiotics could be observed when such combinations were tested against strains of Enterobacteriaceae that produce large amounts of class C beta-lactamases. The minimal inhibitory concentration of the antibiotic of more than 64 mg/L could be decreased to 0.25 mg/L in a 1:4 combination with the inhibitor.

Lack of endothelial nitric oxide synthase aggravates murine pneumococcal meningitis

Nitric oxide (NO) plays a central role in the pathogenesis of bacterial meningitis. However, the role of NO produced by endothelial NO synthase (eNOS) in meningitis is still unclear. We investigated the influence of eNOS depletion on the inflammatory host response, intracranial complications, and outcome in experimental pneumococcal meningitis. Leukocyte accumulation in the cerebrospinal fluid was more pronounced in infected eNOS-deficient mice than in infected wild type mice. This effect could be attributed to an increased expression of P-selectin, macrophage inflammatory protein-2, keratinocyte-derived cytokine, and interleukin (IL)-1beta in the brain of infected eNOS-deficient mice. However, no differences in the cerebral expression of intercellular adhesion molecule-1, tumor necrosis factor-alpha, and IL-6 as well as of neuronal NOS and inducible NOS could be detected between infected wild type and mutant mice. In addition to enhanced leukocyte infiltration into the CSF, meningitis-associated intracranial complications including blood-brain barrier disruption and the rise in intracranial pressure were significantly augmented in infected eNOS-deficient mice. The aggravation of intracranial complications was paralleled by a worsening of the disease, as evidenced by a more pronounced hypothermia, an enhanced weight reduction, and an increased death rate. The current data indicate that eNOS deficiency is detrimental in bacterial meningitis. This effect seems to be related to an increased expression of (certain) cytokines/chemokines and adhesion molecules; thus leading to increased meningeal inflammation and, subsequently, to aggravated intracranial complications.

Acute severe spinal cord dysfunction in bacterial meningitis in adults: MRI findings suggest extensive myelitis

BACKGROUND

Bacterial meningitis is rarely complicated by acute spinal cord involvement (eg, myelitis, ischemic infarction, spinal abscess, or epidural hemorrhage). In spinal cord dysfunction, magnetic resonance imaging (MRI) is the imaging modality of choice. Still, MRI findings of myelitis due to bacterial meningitis in adults have not been reported.

METHODS

Spinal MRIs were obtained during the acute stage of meningitis and on follow-up in 3 adults with bacterial meningitis that was complicated by paraparesis or tetraparesis and bowel and bladder incontinence. The causative pathogens were Streptococcus pneumoniae and Neisseria meningitidis; in 1 patient, the pathogen was not identified.

RESULTS

In all cases, spinal MRI ruled out a compression of the cord by an extramedullary mass but demonstrated hyperintensities on T2-weighted images that predominantly involved the gray matter and extended from the cervical to the lumbar cord. Leptomeningeal and discrete nodular intramedullary enhancement on T1-weighted images was detected only in 1 patient. Follow-up examinations revealed that hyperintensities resolved completely in 1 patient, while a central cavitation developed in the cervical spinal cord of another, and the MRI findings were progressive during the first 4 weeks in the third patient. In all cases, severe paresis and bowel and bladder incontinence persisted.

CONCLUSION

We demonstrate for the first time the MRI findings of adults with acute spinal cord involvement during bacterial meningitis. Magnetic resonance imaging showed central intramedullary hyperintensities on T2-weighted images that extended from the cervical to the lumbar cord, indicating myelitis. Clinical follow-up examinations suggest that myelitis during bacterial meningitis has an unfavorable prognosis.

Ionized and bound calcium inside isolated sarcoplasmic reticulum of skeletal muscle and its significance in phosphorylation of adenosine triphosphatase by orthophosphate

Calcium loading of skeletal muscle sarcoplasmic reticulum performed passively by incubation with high calcium concentrations (0.5--15 mM) on ice gives calcium loads of 50--60 nmol/mg sarcoplasmic reticulum protein. This accumulated calcium is not released by EGTA [ethyleneglycol bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid], but almost completely released by ionophore X-537A plus EGTA or phospholipase A plus EGTA treatment and is therefore assumed to be inside the sarcoplasmic reticulum. This calcium is distributed in one saturable and one non-saturable calcium compartment, as derived from the dependence of the calcium load on the calcium concentration in the medium. These compartments are assigned to bound and ionized calcium inside the sarcoplasmic reticulum, respectively. Maximum calcium binding under these conditions was 33 nmol/mg protein with an apparent half-saturation constant of 5,8 nmol/mg free calcium inside, or between 1.2 and 0.6 mM free calcium inside, assuming an average vesicular water space of 5 or 10 microliter/mg protein, respectively. Calcium-dependent phosphorylation of sarcoplasmic reticulum calcium-transport ATPase from orthophosphate depends on the square of free calcium inside, whilst inhibition of phosphorylation depends on the square of free calcium in the medium. Calcium-dependent phosphorylation appears to be determined by the free calcium concentrations inside or outside allowing calcium binding to the ATPase according to the two classes of calcium binding constants for low affinity calcium binding or high affinity calcium binding, respectively. It is further suggested that the saturation of the low-affinity calcium-binding sites of the ATPase facing the inside of the sarcoplasmic reticulum membrane is responsible for the greater apparent orthophosphate and magnesium affinity in calcium-dependent phosphorylation than in calcium-independent phosphorylation from orthophosphate. Maximum calcium-dependent phosphoprotein formation at 20 degrees C and pH 7.0 is about 4 nmol/mg sarcoplasmic reticulum protein.

A monoclonal antibody to the heavy chain of clathrin

Monoclonal antibodies have been raised to pig brain triskelions and one clone, DC41, was found to recognize the clathrin heavy chain by immunoblotting. However, both by immunofluorescence and immunoelectron microscopy, and in complete contrast to polyclonal anti-clathrin antibodies, monoclonal DC41 did not label either coated pits or coated vesicles anywhere in the cell. Instead it appeared to label the cell cytoplasm. These data suggest that DC41 recognizes a cytoplasmic form of clathrin, perhaps that form produced by uncoating of coated vesicles which is then ready to re-build another coated pit.

Comparison of the TEMPO+ ear-level speech processor and the cis pro+ body-worn processor in adult MED-EL cochlear implant users

A study was conducted to compare the new MED-EL TEMPO+ ear-level speech processor with the CIS PRO+ body-worn processor in the COMBI 40/COMBI 40+ implant system. Speech tests were performed in 46 experienced subjects in two test sessions approximately 4 weeks apart. Subjects were switched over from the CIS PRO+ to the TEMPO+ in the first session and used only the TEMPO+ in the time between the two sessions. Speech tests included monosyllabic word tests and sentence tests via the telephone. An adaptive noise method was used to adjust each subject's scores to approximately 50%. Additionally, subjects had to complete a questionnaire based on their 4 weeks of experience with the TEMPO+. The speech test results showed a statistically significant improvement in the monosyllabic word scores with the TEMPO+. In addition, in the second session, subjects showed a significant improvement when using the telephone with the TEMPO+, indicating some learning in this task. In the questionnaire, the vast majority of subjects found that the TEMPO+ allows equal or better speech understanding and rated the sound quality of the TEMPO+ higher. All these objective and subjective results indicate the superiority of the TEMPO+ and are mainly attributed to a new coding strategy called CIS+ and its implementation in the TEMPO+. In other words, based on the results of this study, it appears that after switching over from the CIS PRO+ to the TEMPO+, subjects are able to maintain or even improve their own speech understanding capability.

Comparative investigations of algorithms for the detection of breaths in newborns with disturbed respiratory signals

The correct detection of the beginning of inspiration and expiration in the respiratory signals is an essential prerequisite for accurate lung function testing in newborns. Five algorithms for breath detection using pneumotachographically measured flow and volume signals were investigated with regard to the error rate. To compare and to evaluate the reliability of these algorithms 12 minimally and 12 severely disturbed flow and volume signals from spontaneously breathing newborns were used. With the exception of an algorithm based on Walsh-transformed signals, all algorithms work reliably (error rate <1.1%) if disturbances are minimal. In severely disturbed signals there is a great difference between the algorithms. The most robust algorithm tested (trigger of the flow signal with an additional plausibility check of the recognized breath) resulted in an error rate of <3.4%. Not all algorithms tested are suitable for real-time applications because they differ considerably in delay time for breath detection.

Aspects of the mechanism of action of local anesthetics on the sarcoplasmic reticulum of skeletal muscle

1. The effect was studied of local anesthetics (tetracaine, dibucaine, procaine and xylocaine) on the forward and the backward reactions of the calcium pump of skeletal muscle sarcoplasmic reticulum. 2. The inhibition of the rate of calcium uptake, the rate of calcium-dependent ATP splitting and the rate of calcium-dependent ATP-ADP phosphate exchange by sarcoplasmic reticulum in the presence of the above drugs is at least partially due to the inhibition of the phosphoprotein formation from ATP. 3. The rate of the ADP-induced calcium release from sarcoplasmic reticulum and the rate of ATP synthesis driven by the calcium efflux are inhibited on account of a reduction of the phosphoprotein formation by orthophosphate. 4. The phosphorylation of calcium transport ATPase by either ATP or orthophosphate is diminished by the local anesthetics owing to a reduction in the apparent calcium affinity of sarcoplasmic reticulum emmbranes on the outside and on the inside, respectively. 5. The drug-induced calcium efflux from calcium-preloaded sarcoplasmic reticulum vesicles, a reaction not requiring ADP, is probably not mediated by calcium transport ATPase.

Cross-linking of bromodeoxyuridine-substituted oligonucleotides to the EcoRI and EcoRV restriction endonucleases

We have synthesized several self-complementary oligodeoxynucleotides which contain bromodeoxyuridine in various positions within and outside of the recognition sequence for the EcoRI and EcoRV restriction endonucleases. These oligodeoxynucleotides are cleaved in the presence of Mg2+ by their respective enzyme. Upon irradiation by long-wavelength ultraviolet light and in the absence of Mg2+ they are cross-linked in low yield to their enzymes, forming 1:1 and 1:2 (oligodeoxynucleotide:enzyme subunit) adducts. Cross-linking occurs with both specific and non-specific complexes. With EcoRI the site of cross-linking was determined to be at or close to Met-137, i.e. in a region of the molecule implicated by other studies from our laboratory [Scholtissek et al. (1986) J. Biol. Chem. 261, 2228-2234] in the binding and cleavage of the substrate.

Reciprocal changes in endothelial and inducible nitric oxide synthase expression following carotid angioplasty in the pig

OBJECTIVE

Nitric oxide produced by nitric oxide synthase appears to have an important role in the regulation of arterial tone, platelet adhesion and smooth muscle cell proliferation. Our aim was to investigate the effects of balloon angioplasty on expression of endothelial NO synthase (cNOS) and inducible NO/synthase (iNOS) in the pig carotid artery and to relate any changes in expression to the processes of reendothelialisation and vascular repair.

METHODS

Pigs were sacrificed at various time points to follow NOS expression in the neointima, media and regenerated endothelium. Immunocytochemical staining was used to localize cNOS and iNOS expression in the vessel wall. Relative amounts of cNOS were measured using quantitative in vitro alitoradiography. cNOS mRNA and iNOS mRNA was quantified by competitive PCR based on the sequenced cDNA of porcine cNOS and iNOS.

RESULTS

Uninjured carotid arteries exhibited dense uniform luminal endothelial staining for cNOS. Balloon angioplasty caused denudation of cNOS immunoreactive cells and a marked reduction of cNOS gene expression but a complete recovery was noted by day 35. In normal uninjured carotid arteries no evidence of iNOS immunoreactivity was demonstrable but 24 h after injury, marked homogeneous iNOS immunoreactivity was detected in medial vascular smooth muscle cells. By 5 days, staining was evident in cells within the forming neointimal layer with no evidence of iNOS immunoreactivity in the media. iNOS immunoreactivity persisted in cells at the luminal surface at 7 days and iNOS gene expression appeared to be sustained in some animals with ruptured internal elastic lamina at 21 days.

CONCLUSION

Balloon injury is associated with de-endothelialisation and a marked reduction in cNOS gene expression and activity. iNOS is induced throughout the arterial media within VSMC soon after balloon injury and persists for up to 21 days. These observations imply an important regulatory role for locally generated NO in the pathophysiological response to balloon injury.

Superantigen overcomes resistance of IL-6-deficient mice towards MOG-induced EAE by a TNFR1 controlled pathway

Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein peptide 35-55 (MOG) leads to a chronic form of disease characterized by demyelination, inflammation and gliosis in the central nervous system (CNS). Recently IL-6 and LT alpha were found to be required for induction of the disease. The main features associated with EAE resistance of IL-6(-/-) and LT alpha(-/-) mice were reduced T cell proliferation and endothelial activation. As shown here treatment of MOG-immunized IL-6(-/-) mice with staphylococcal enterotoxin B (SEB)reversed their resistance to MOG-induced EAE. SEB failed to restore susceptibility to EAE in LT alpha(-/-) mice. The effect of SEB to induce EAE in IL-6(-/-) mice depends on TNF receptor type 1 (TNFR1) signaling because IL-6/TNF/LT alpha(-/-) and IL-6/TNFR1(-/-) are refractory to SEB. TNFR1 is involved in SEB induced trafficking of T cells into the CNS as evidenced by the failure to up-regulate VCAM-1 on CNS endothelium and lack of accumulation of V beta 8(+) T cells in the CNS of IL-6/TNFR1(-/-) mice upon immunization with MOG and treatment with SEB. The course of SEB triggered EAE in MOG immunized IL-6(-/-) mice was characterized by reduced severity and duration of clinical manifestations, which were associated with a significant drop of CNS infiltrating neutrophils and MIP-2 expression after peak disease. Taken collectively the effect of SEB to overcome EAE resistance points to a transient IL-6 independent but TNFR1 dependent proinflamatory pathway in EAE pathogenesis and suggests a crucial function for IL-6 in disease perpetuation.

Comparison between the impact of morning and evening doses of rivaroxaban on the circadian endogenous coagulation rhythm in healthy subjects

ESSENTIALS: It is unknown whether single rivaroxaban doses should best be administered in the morning or evening. Circadian rhythm of coagulation/fibrinolysis was measured after morning or evening intake of rivaroxaban. Evening intake of rivaroxaban leads to prolonged exposure to rivaroxaban concentrations. Evening intake of rivaroxaban better matches the morning hypofibrinolysis.

BACKGROUND

A circadian variation of the endogenous coagulation system exists with hypercoagulability and hypofibrinolysis and a corresponding peak of cardiovascular thromboembolic events in the morning. So far, no information is given as to whether single daily doses of the new oral anticoagulant drug rivaroxaban should best be administered in the morning or the evening.

MATERIALS AND METHODS

Sixteen healthy male or female volunteers with a mean age of 26 ± 7 years were included in this randomized, controlled, analyst-blinded cross-over clinical trial. All subjects were given three morning and three evening single doses of 10 mg rivaroxaban. Circadian rhythms of prothrombin fragment 1 + 2, plasminogen activator inhibitor, and plasmin-antiplasmin complex were measured before any medication intake, as well as after morning or evening medication intake. Rivaroxaban concentrations were determined by an anti-activated factor X assay and liquid chromatography-mass spectrometry.

MAIN RESULTS

Concentrations of rivaroxaban were higher 12 h after evening intake of rivaroxaban than 12 h after morning intake (53.3 ng mL(-1) [95% confidence interval 46.0-67.8] vs. 23.3 ng mL(-1) [19.4-29.1, respectively]). Rivaroxaban intake in the evening reduced morning F1+2 concentrations better at 8:00 AM than did administration on awakening (85 ± 25 nmol L(-1) vs. 106 ± 34 nmol L(-1) , CI: 9.4-32.1). In addition, this suppression effect was longer lasting after evening intake.

CONCLUSIONS

Evening intake of rivaroxaban leads to prolonged exposure to rivaroxaban concentrations and better matches the morning hypofibrinolysis. These results might help to further improve the efficacy and safety of rivaroxaban treatment.

Pamidronate increases bone mineral density in women with postmenopausal or steroid-induced osteoporosis

INTRODUCTION

We aimed to determine the efficacy and safety of a cyclic intravenous therapy with pamidronate in patients with postmenopausal or glucocorticoid-induced osteoporosis.

METHODS

We enrolled 86 Austrian female patients with postmenopausal (n = 69, mean age 68.13 +/- 1.14) or glucocorticoid-induced (n = 17, mean age 66.89 +/- 2.03) osteoporosis defined as a T-score of < -2.5 for bone mineral density (BMD) of the lumbar spine L1-L4. Patients received a single intravenous dose of 30 mg pamidronate at 3 months intervals. The per cent change in BMD was primary, whereas the safety and the biological response were secondary endpoints.

RESULTS

Seventy-six female patients (88%) completed study. Sixty patients received pamidronate therapy for the treatment of late postmenopausal osteoporosis and 16 patients received the same treatment for glucocorticoid-induced osteoporosis. At the end of the trial, lumbar spine (L1-L4) BMD increased significantly in patients with postmenopausal osteoporosis (P = 0.000067), whereas in patients with glucocorticoid-induced osteoporosis no significant change was observed (P = 0.724). The increase in the Ward's triangle BMD did not reach significance level in postmenopausal women receiving pamidronate (P = 0.0740). However, pamidronate treatment for glucocorticoid-induced osteoporosis resulted in a significant increase in Ward's triangle BMD (P = 0.0029). The efficacy of pamidronate treatment for postmenopausal osteoporosis was also reflected in a decrease in circulating biochemical markers for bone formation, including alkaline phosphatase and osteocalcin. In addition, pamidronate was well tolerated with no incidence of severe gastrointestinal events.

CONCLUSION

Cyclic intravenous administration of pamidronate is well-tolerated therapy in postmenopausal osteoporosis, and increases spinal BMD. Randomized controlled studies with adequate number of patients are needed to test the efficacy of the compound in the treatment of glucocorticoid-induced osteoporosis.

Digital pulse plethysmography as a non-invasive method for predicting drug-induced changes in left ventricular preload

OBJECTIVE

Changes in the contour of the plethysmographically recorded digital pulse curve after nitrate ingestion are well known, but it has not been fully established whether these changes reflect nitrate action on left ventricular (LV) preload or afterload. Therefore, we compared the pulse wave contour after administration of equieffective doses of nitroglycerin and nifedipine.

METHODS

In 20 patients with coronary artery disease we measured aortic blood pressure curve in the aorta ascendens, digital volume pulse curve with a photoelectric pulse pickup, Riva Rocci blood pressure and heart rate after administration of either 0.8 mg nitroglycerin or 10 mg nifedipine.

RESULTS

Peak plasma concentrations of nitroglycerin and nifedipine were achieved 5 min and 20 min after ingestion of the drugs. Systolic aortic blood pressure decreased after both nitroglycerin and nifedipine to 19.4 mmHg, but diastolic blood pressure decreased only after nifedipine by 10.5 mmHg (P < 0.05). Riva Rocci blood pressures showed a similar time course. Heart rate increased from 67.4 to 70.9 beats.min-1 after nitroglycerin and from 58.9 to 69.4 beats.min-1 after nifedipine. The calculated a/b ratio of the aortic pressure curve increased after both medications (nitroglycerin, from 1.66 to 1.99; nifedipine, from 1.66 to 1.93) and its time course mimicked that of the systolic blood pressure. The a/b ratio of the digital pulse curve did not change after nifedipine, but showed a pronounced rise after nitroglycerin from 1.29 to 1.84. With regard to pharmacological actions, nitroglycerin causes a reduction in LV preload and afterload, whereas nifedipine has only LV-afterload-reducing activity.

CONCLUSION

We conclude, that the reduction in afterload did not cause the typical changes in wave contour of the peripheral pulse curve which occur with organic nitrates. Most likely changes in the a/b ratio reflect changes in LV preload.

Structural and functional insights into the AmtB/Mep/Rh protein family

X-ray crystallography revealed a similar architecture of the ammonium transport protein AmtB from Escherichia coli and the homologous protein Amt-1 from Archaeoglobus fulgidus. Furthermore, the atomic structures suggest that the proteins conduct ammonia (NH3) rather than ammonium ions (NH4+). These findings indicate that the more than 350 members of the ammonium transporter/methylamine permease/Rhesus (Amt/Mep/Rh) protein family found in archaea, bacteria, fungi, plants and animals are ammonia-conducting channels rather than ammonium ion transporters. The essential part of these proteins is the narrow hydrophobic ammonia-conducting pore with two highly conserved histidine residues located in the middle of the pore. A specific ammonium ion binding site is found at the extracellular entry site of E. coli AmtB. E. coli AmtB and its regulator GlnK form an effective ammonium sensory system that couples intracellular gene regulation by the nitrogen control system to external changes in ammonium availability. Based on structural and functional analysis of various mutants, two conserved histidine residues were found to be essential for substrate conductance also in the functional eukaryotic ammonium transporters. The next big challenge in the field surely is to determine the atomic structure of Rh proteins.