The nipah virus fusion protein is cleaved within the endosomal compartment

Nipah virus (NiV) is a recently emerged and highly pathogenic paramyxovirus that causes a systemic infection in animals and humans and can infect a wide range of cultured cells. Interestingly, the NiV fusion (F) protein has a single arginine at the cleavage site similar to paramyxoviruses that are activated by exogenous trypsin-like enzymes only present in specific cells and tissues and therefore only cause localized infections. We show here that NiV F activation is not mediated by an exogenous serum protease but by an endogenous ubiquitous cellular protease after endocytosis of the protein. In addition to endocytosis, acidification of the endosome is a prerequisite for F cleavage. These results show that activation of the NiV F protein depends on a type of proteolytic cleavage that is clearly different from what is known for other paramyxoviral and orthomyxoviral fusion proteins. To our knowledge, this is the first example of a viral class I fusion protein whose activation depends on clathrin-mediated constitutive endocytosis.

[Lung cancer screening -- state of the art]

Besides smoking as the main risk factor for lung cancer several occupational risk factors like exposure to asbestos, polycyclic aromatic hydrocarbons, uranium and dust containing nickel or silica have to be considered. Due to lack of effort in smoking prevention and cessation, lung cancer screening is an important issue. A number of pitfalls has to be considered when evaluating the efficacy of screening procedures. In this paper, we summarize the results of the major studies including chest X-ray, sputum cytology and low dose computed tomography. Randomized controlled studies involving low dose CT in about 100 000 subjects are on the way. Around the year 2010 we will be able to define whether or not lung cancer screening including new techniques and standardized algorithms yields a decrease in mortality. If diagnostic algorithms are used which have been applied in published feasibility studies, the mean percentage of invasive diagnostic measures revealing benign lesions is about 34 % and thus below those obtained in, e. g., breast cancer screening trials.

Endocytosis of the Nipah virus glycoproteins

Nipah virus (NiV), a highly pathogenic member of the family Paramyxoviridae, encodes the surface glycoproteins F and G. Since internalization of the NiV envelope proteins from the cell surface might be of functional importance for viral pathogenesis either by regulating cytopathogenicity or by modulating recognition of infected cells by the immune system, we analyzed the endocytosis of the NiV F and G proteins. Interestingly, we found both glycoproteins to be internalized in infected and transfected cells. As endocytosis is normally mediated by tyrosine- or dileucine-dependent signals in the cytoplasmic tails of transmembrane proteins, all potential internalization signals in the NiV glycoproteins were mutated. Whereas the G protein appeared to be constitutively internalized with the bulk flow during membrane turnover, uptake of the F protein was found to be signal mediated. F endocytosis clearly depended on a membrane-proximal YXXPhi motif and was found to be of functional importance for the biological activity of the protein.

[Percutaneous ablation of pulmonary tumours: state-of-the-art 2004]

Percutaneous radiofrequency ablation (RFA) and laser-induced interstitial thermotherapy (LITT) are well established since many years in liver and other soft tissue tumors. During the past 2 years there are increasing reports on applications in pulmonary tumors. There are, however, numerous differences to ablations in other organs: indications in pulmonary metastases and lung cancer have to be balanced against the specific possibilities of well-established surgical resections. Tissue specific features require different concepts of energy deployment and complications and methods for assessment of therapeutic effectiveness vary from other applications. Other aspects, however, are quite clear, yet. There are specific established indications particularly for thermoablation of pulmonary metastases. Tumor ablation is easily performed by experienced interventional radiologists and serious complications are rare. Patient acceptance is good. Further studies are required on indications, technical requirements, therapy control and particularly long-term results.

Ubiquitous activation of the Nipah virus fusion protein does not require a basic amino acid at the cleavage site

Nipah virus (NiV), a highly pathogenic paramyxovirus, causes a systemic infection in vivo and is able to replicate in cultured cells of many species and organs. Such pantropic paramyxoviruses generally encode fusion (F) proteins with multibasic cleavage sites activated by furin or other ubiquitous intracellular host cell proteases. In contrast, NiV has an F protein with a single arginine (R109) at the cleavage site, as is the case with paramyxoviruses that are activated by trypsin-like proteases only present in specific cells or tissues and therefore only cause localized infections. Unlike these viruses, cleavage of the NiV F protein is ubiquitous and does not require the addition of exogenous proteases in cell culture. To determine the importance of the amino acid sequence at the NiV F protein cleavage site for ubiquitous activation, we generated NiV F proteins with mutations around R109. Surprisingly, neither the exchange of amino acids upstream of R109 nor replacement of the basic residue itself interfered with F cleavage. Thus, R109 is not essential for F cleavage and activation. Our data demonstrate that NiV F-protein activation depends on a novel type of proteolytic cleavage that has not yet been described for any other paramyxovirus F protein. NiV F activation is mediated by a ubiquitous protease that requires neither a monobasic nor a multibasic cleavage site and therefore differs from the furin- or trypsin-like proteases known to activate other ortho- and paramyxovirus fusion proteins.

[Radiological diagnosis of pulmonary metastases: imaging findings and diagnostic accuracy]

Pulmonary metastases typically present as mostly multiple and bilateral, well-defined, non-calcified pulmonary nodules with predominantly basal and peripheral location. Ill-defined, cavitating, calcified and endobronchial metastases are uncommon. In the absence of pathognomonic findings precise differentiation from other-even benign-pulmonary nodules is almost impossible. Demonstration of contrast enhancement at CT or MRI or evidence of growth at serial examinations support the diagnosis of pulmonary metastases. In uncertain cases percutaneous fine-needle aspiration or cutting needle biopsy will allow diagnosis with acceptable risk of complications and patient discomfort. The only relatively common complication of pneumothorax can and should be controlled by the interventional radiologist by aspiration or drainage.

Diagnostic Performance of a Commercially Available Computer-aided Diagnosis System for Automatic Detection of Pulmonary Nodules: Comparison with Single and Double Reading

OBJECTIVE

To assess the diagnostic performance of a commercially available computer-aided diagnosis (CAD) system for automatic detection of pulmonary nodules with multi-row detector CT scans compared to single and double reading by radiologists.

MATERIALS AND METHODS

A CAD system for automatic nodule detection (Siemens LungCare NEV VB10) was applied to four-detector row low-dose CT (LDCT) performed on nine patients with pulmonary metastases and compared to the findings of three radiologists. A standard-dose CT (SDCT) was acquired simultaneously and used for establishing the reference data base. The study design was approved by the Institutional Review Board and the appropriate German authorities. The reference data base consisted of 457 nodules (mean size 3.9 +/- 3.1 mm) and was established by fusion of the sets of nodules detected by three radiologists independently reading LDCT and SDCT and by CAD. An independent radiologist used thin slices to eliminate false positive findings from the reference base.

RESULTS

An average sensitivity of 54 % (range 51 % to 55 %) was observed for single reading by one radiologist. CAD demonstrated a similar sensitivity of 55 %. Double reading by two radiologists increased the sensitivity to an average of 67 % (range 67 % to 68 %). The difference to single reading was significant (p < 0.001). CAD as second opinion after single reading increased the sensitivity to 79 % (range 77 % to 81 %), which proved to be significantly better than double reading (p < 0.001). CAD produced more false positive results (7.2 %) than human readers but it was acceptable in clinical routine.

CONCLUSION

Double reading with CAD as second reader offered a significantly increased sensitivity compared to conventional double reading. Thus, CAD is a valuable tool for the detection of pulmonary nodules and should be used as second opinion.

Endogenous and exogenous glucocorticoids decrease plasma ghrelin in humans

OBJECTIVE

The orexigenic and adipogenic peptide hormone ghrelin is predominantly produced and secreted by the stomach and seems to transduce changes in food intake to specific neuronal circuits in the brain. The activity of ghrelin also includes stimulatory effects on the corticotropic system. However, little is known about the influence of glucocorticoids on ghrelin levels. We therefore studied human plasma ghrelin levels in the presence and absence of elevated glucocorticoid levels of either endogenous or exogenous origin.

METHODS

Plasma ghrelin levels were measured in five patients with chronic hypercortisolism (aged 29-58, median 46 years) due to Cushing's syndrome before and after successful surgery for the adenoma, and in eight healthy controls (aged 24-39, median 27.5 years) before and after 30 mg prednisolone (for 5 days) once a day in the morning (median body mass index (BMI) 22.7 kg/m(2)). Plasma ghrelin levels were measured with a commercially available radioimmunoassay.

RESULTS

In patients with Cushing's syndrome, plasma ghrelin levels were low (median 363.2 pg/ml, range 161.9-525.7 pg/ml) and significantly increased by 26.6% (P=0.04) after successful surgery, while BMI decreased (median 26.2-24.0 kg/m(2), P=0.04). A strong negative correlation (r=-0.9, P=0.04) between changes in BMI and plasma ghrelin was observed. In healthy controls, plasma ghrelin levels (median 288.7 pg/ml, range 119.6-827.8 pg/ml) were significantly suppressed by 18.3% (P=0.04) after prednisolone treatment.

CONCLUSIONS

We have shown for the first time that plasma ghrelin levels are decreased under endogenously or exogenously induced hypercortisolism, making ghrelin an unlikely candidate for causing the changes in energy balance or body composition characteristic of Cushing's disease. However, the reduced ghrelin secretion could reflect a compensation mechanism in reaction to the metabolic consequences of chronic hypercortisolism.

Pharmacodynamics and pharmacokinetics of synthetic mineralocorticoids and glucocorticoids: receptor transactivation and prereceptor metabolism by 11beta-hydroxysteroid-dehydrogenases

Glucocorticoid (GC) and mineralocorticoid (MC) action in target tissues is determined by prereceptor metabolism by 11beta-hydroxysteroid-dehydrogenases (HSDs) and receptor transactivation. We characterized these parameters for steroids often used in clinical practice. HSD activity was examined in human liver (HSD1) and kidney microsomes (HSD2) and in CHO cells stably transfected with both enzymes. GC and MC transcriptional activity was tested by luciferase assay in CV-1 cells transfected with human GC or MC receptor expression vectors. The 11-hydroxy-group is necessary for GC and MC receptor transactivation. As HSD2 oxidizes 11-hydroxysteroids to inactive 11-dehydrosteroids, GC and MC activity in HSD2-expressing tissues (kidney, colon) is regulated by this enzyme. As 9alpha-fluorination (such as in 9alpha-fluorocortisol) decreases oxidation by HSD2 and increases both GC and MC receptor transactivation, this modification leads to optimal, but non-selective transactivation of both receptors. Increased GC receptor and decreased MC receptor transactivation leading to more selective GC activity is reached using the following substituents: 16beta-methyl (in betamethasone), 16alpha-methyl (in dexamethasone) and triangle up 1-dehydro-configuration (in prednisolone). Whereas the modifications in position 16 decrease oxidation by HSD2, the triangle up 1-dehydro-configuration increases HSD2-activity leading to an enhanced inactivation of prednisolone compared to all other steroids. 9alpha-fluorocortisol, the most frequently used substance for MC-substitution, seems to be the best choice of available steroids for this purpose. Whereas GC selectivity can be improved by hydrophobic substituents in position 16 and the triangle up 1-dehydro-configuration, maximal GC activity needs additional fluorination in position 9alpha (such as in dexamethasone). For GC therapy directed to HSD2-expressing organs, widely used prednisolone does not seem to be the optimal recommendation.

The role of progesterone metabolism and androgen synthesis in renal blood pressure regulation

11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) plays a crucial role in converting hormonally active cortisol into inactive cortisone, conferring specificity onto the human mineralocorticoid receptor (MR). Progesterone binds with even higher affinity to the MR, but acts as an MR antagonist. How aldosterone is able to keep its function as predominant MR ligand in clinical situations with high progesterone concentrations, such as pregnancy, is not clear. We have shown in vitro that the human kidney possesses an effective enzyme system that metabolizes progesterone to inactive metabolites in a process similar to the inactivation of cortisol by 11beta-HSD2. In studies on patients with adrenal insufficiency, we have shown that the in vivo anti-mineralocorticoid activity of progesterone is diminished by inactivating metabolism of progesterone, local formation of the deoxycorticosterone mineralocorticoid from progesterone, and inhibition of 11beta-HSD2 by progesterone and its metabolites resulting in decreased inactivation of cortisol and hence increased MR binding by cortisol. The enzymes involved in progesterone metabolism are also responsible for the capability of the human kidney to convert pregnenolone to DHEA and androstenedione leading to the formation of active androgens, testosterone and 5alpha-DH-testosterone. Locally produced androgens might be responsible for the observed difference in blood pressure between men and women and higher susceptibility to hypertension in men.

Renal inactivation, mineralocorticoid generation, and 11beta-hydroxysteroid dehydrogenase inhibition ameliorate the antimineralocorticoid effect of progesterone in vivo

Progesterone (P) is a strong mineralocorticoid receptor (MR) antagonist in vitro. The high P concentrations seen in normal pregnancy only moderately increase renin and aldosterone concentrations. In previous in vitro studies we hypothesized that this may be explained by intrarenal conversion of P to less potent metabolites. To investigate the in vivo anti-MR potency of P, we performed an infusion study in patients with adrenal insufficiency (n = 8). They omitted 9alpha-fluorocortisol for 4 d and hydrocortisone for 0.5 d before a continuous iv infusion of aldosterone for 8.5 h, with an additional iv P infusion commenced at 4 h. During aldosterone infusions the initially elevated urinary sodium to potassium ratio decreased significantly. Despite the 1000-fold excess of P over aldosterone, the urinary sodium to potassium ratio and urinary sodium excretion increased only slightly after 3 h of P infusion. We detected inhibition of renal 11beta-hydroxysteroid dehydrogenase type 2 by P, thus giving cortisol/prednisolone access to the MR. Urinary and plasma concentrations of 17alpha-hydroxyprogesterone, a major metabolite of renal P metabolism, and those of serum androstenedione and deoxycorticosterone, a mineralocorticoid itself, increased significantly during P infusion. This supports the hypothesis of an effective protection of the MR from P by efficient extraadrenal downstream conversion of P.