The archaeome in metaorganism research, with a focus on marine models and their bacteria-archaea interactions

Metaorganism research contributes substantially to our understanding of the interaction between microbes and their hosts, as well as their co-evolution. Most research is currently focused on the bacterial community, while archaea often remain at the sidelines of metaorganism-related research. Here, we describe the archaeome of a total of eleven classical and emerging multicellular model organisms across the phylogenetic tree of life. To determine the microbial community composition of each host, we utilized a combination of archaea and bacteria-specific 16S rRNA gene amplicons. Members of the two prokaryotic domains were described regarding their community composition, diversity, and richness in each multicellular host. Moreover, association with specific hosts and possible interaction partners between the bacterial and archaeal communities were determined for the marine models. Our data show that the archaeome in marine hosts predominantly consists of Nitrosopumilaceae and Nanoarchaeota, which represent keystone taxa among the porifera. The presence of an archaeome in the terrestrial hosts varies substantially. With respect to abundant archaeal taxa, they harbor a higher proportion of methanoarchaea over the aquatic environment. We find that the archaeal community is much less diverse than its bacterial counterpart. Archaeal amplicon sequence variants are usually host-specific, suggesting adaptation through co-evolution with the host. While bacterial richness was higher in the aquatic than the terrestrial hosts, a significant difference in diversity and richness between these groups could not be observed in the archaeal dataset. Our data show a large proportion of unclassifiable archaeal taxa, highlighting the need for improved cultivation efforts and expanded databases.

Transcriptional response of the calcification and stress response toolkits in an octocoral under heat and pH stress

Up to one-third of all described marine species inhabit coral reefs, but the future of these hyperdiverse ecosystems is insecure due to local and global threats, such as overfishing, eutrophication, ocean warming and acidification. Although these impacts are expected to have a net detrimental effect on reefs, it has been shown that some organisms such as octocorals may remain unaffected, or benefit from, anthropogenically induced environmental change, and may replace stony corals in future reefs. Despite their potential importance in future shallow-water coastal environments, the molecular mechanisms leading to the resilience to anthropogenically induced stress observed in octocorals remain unknown. Here, we use manipulative experiments, proteomics and transcriptomics to show that the molecular toolkit used by Pinnigorgia flava, a common Indo-Pacific gorgonian octocoral, to deposit its calcium carbonate skeleton is resilient to heat and seawater acidification stress. Sublethal heat stress triggered a stress response in P. flava but did not affect the expression of 27 transcripts encoding skeletal organic matrix (SOM) proteins. Exposure to seawater acidification did not cause a stress response but triggered the downregulation of many transcripts, including an osteonidogen homologue present in the SOM. The observed transcriptional decoupling of the skeletogenic and stress-response toolkits provides insights into the mechanisms of resilience to anthropogenically driven environmental change observed in octocorals.

Drug-induced confusional states: the usual suspects?

BACKGROUND

Acute confusional state (ACS) is a frequent reason for hospital admission. This study examines retrospectively the frequency by which individual drugs were found responsible for ACS.

RESULTS

Drug-induced ACS was found in 65 (18.8%) of 346 hospital admissions for acute confusion. The most frequent causative substances were dopaminergic drugs in Parkinsonian patients (24.2%), diuretics (15.1%), tricyclic or tetracyclic antidepressants (13.6%) and benzodiazepines (13.6%). Almost half of the patients were demented, and in one-third of these, dementia had not been diagnosed hitherto.

CONCLUSION

The data suggest that diuretics by way of causing hyponatraemia are as relevant a cause of ACS as dopaminergic or anticholinergic substances.

[Neuroendocrine tumors of the stomach (gastric carcinoids) are on the rise: good prognosis with early detection]

Neuroendocrine tumors (NET) of the stomach are on the rise. In the United States they have increased about tenfold in the last 35 years. Prognosis has been much improved over the last three to four decades. Nowadays most of such NETs are diagnosed at an early stage. Quite often gastric NETs are found incidentally during a gastroscopy, performed for other reasons. Most of the asymptomatic, well differentiated gastric NETs are less than 2 cm in diameter. Conservative management and endoscopic surveillance is adequate for well differentiated, multifocal type 1 or type 2 gastric NETs (gastric carcinoids) of 10-20 mm , unless they are angio-invasive, have infiltrated into the muscularis propria or have metastasized. Endoscopic ultrasound is the method of choice to determine tumor size and depth of infiltration. Surgery is, however, indicated for all NETs larger than 20 mm. For optimal management tumor biology, type and stage of the neoplasm as well as the individual situation of the patient have to be taken into account. Most of the patients can be treated conservatively and be followed up with endoscopic surveillance.

Correlations between clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in the cardiac Na+ channel

Aim:

We compared the clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in domain II (S5-S6) of human, hNa_v1.5, cardiac Na⁺ channels.

Methods:

Full clinical evaluation of pedigree members through three generations of a Chinese family combined with SCN5A sequencing from genomic DNA was compared with patch and voltage-clamp results from two independent expression systems.

Results:

The four mutation carriers showed bradycardia, and slowed sino-atrial, atrioventricular and intraventricular conduction. Two also showed sick sinus syndrome; two had ST elevation in leads V1 and V2. Unlike WT-hNa_v1.5, whole-cell patch-clamped HEK293 cells expressing R878C-hNa_v1.5 showed no detectable Na⁺ currents (i_Na), even with substitution of a similarly charged lysine residue. Voltage-clamped Xenopus oocytes injected with either 0.04 or 1.5 μg μL⁻¹ R878C-hNa_v1.5 cRNA similarly showed no i_Na, yet WT-hNa_v1.5 cRNA diluted to 0.0004–0.0008 ng μL⁻¹resulted in expression of detectable i_Na. i_Na was simply determined by the amount of injected WT-hNa_v1.5: doubling the dose of WT-hNa_v1.5 cRNA doubled i_Na. i_Na amplitudes and activation and inactivation characteristics were similar irrespective of whether WT-hNa_v1.5 cRNA was given alone or combined with equal doses of R878C-hNa_v1.5 cRNA therefore excluding dominant negative phenotypic effects. Na⁺ channel function in HEK293 cells transfected with R878C-hNa_v1.5 was not restored by exposure to mexiletine (200 μm) and lidocaine (100 μm). Fluorescence confocal microscopy using E3-Nav1.5 antibody demonstrated persistent membrane expression of both WT and R878C-hNa_v1.5. Modelling studies confirmed that such i_Na reductions reproduced the SSS phenotype.

Conclusion:

Clinical consequences of the novel R878C mutation correlate with results of physiological studies.

K(ATP) channel current increases in postinfarction remodeled cardiomyocytes

Adenosintriphosphate-sensitive potassium channels (K(ATP) channels) are an important linkage between the metabolic state of a cell and electrophysiological membrane properties. In this study, K(ATP) channels were studied in myocytes of normal and remodeled myocardium of the rat. Myocardial infarction was induced by ligature of the left anterior descending artery. Remodeled myocytes were obtained from the hypertrophied posterior left ventricular wall and interventricular septum 3 months after infarction. The current through K(ATP) channels was measured in whole-cell and inside-out patches by using the patch-clamp technique. After myocardial infarction, the heart weight/body weight ratio was doubled and the myocytes were hypertrophied yielding a cell capacitance of 266+/-16 pF compared to 122+/-12 pF in control cells. The amount of Kir6.2 protein was indistinguishable in corresponding regions of control and remodeled hearts. The ATP sensitivity of K(ATP) channels in remodeled cells was significantly lower than in control cells (half maximum block at 115 micromol/l ATP in remodeled and at 71 mumol/l ATP in control cells). The maximum I (KATP) density induced by metabolic inhibition was higher in small remodeled (176+/-15 pA/pF) than in control cells (127+/-11 pA/pF), but was unchanged in large remodeled cells. Both, the higher I (KATP) density and the lower sensitivity of the K(ATP) channels to ATP suggest that remodeled cardiomyocytes develop an improved tolerance to ischemia by stabilizing the resting potential and decreasing excitability.

Contribution of neuronal sodium channels to the cardiac fast sodium current is greater in dog heart Purkinje fibers than in ventricles

OBJECTIVE

To determine the presence and the potential contribution of neuronal sodium channels to dog cardiac function.

METHODS

We used a combination of electrophysiological (patch clamp), RT-PCR, biochemical and immunohistochemical techniques to identify and localize neuronal Na(+) channels in dog heart and determine their potential contribution to the fast sodium current.

RESULTS

In all cardiac tissues investigated, Na(v)1.1, Na(v)1.2 and Na(v)1.3 transcripts were detected. In immunoblots, we found Na(v)1.1 and Na(v)1.2 proteins in the ventricle (V) and in Purkinje fibers (PF). Na(v)1.3 immunoblots suggested strong proteolytic activity against this isoform in the heart. Na(v)1.6 was not found in any of the tissues tested. Confocal immunofluorescence on cardiac myocytes showed that Na(v)1.1 was predominantly localized at the intercalated disks in V and PF and around the nucleus (V). Na(v)1.2 was only present at the Z lines (V). Consistent with the immunoblot data, an intense but diffuse intracellular staining was observed for Na(v)1.3. Na(v)1.6 fluorescence staining was faint and diffuse. Surprisingly, immunoblots indicated the presence of two Na(v)beta 2 variants: a 42-kDa protein that co-localized with Na(v)1.2 at the Z lines in V and a 34-kDa protein that co-localized with Na(v)1.1 at the intercalated disks in PF. In agreement with the biochemical data, electrophysiological results suggest that neuronal sodium channels generate 10+/-5% and 22+/-5% of the peak sodium current in dog ventricle and Purkinje fibers, respectively.

CONCLUSIONS

Our results suggest that neuronal NaChs are more abundant in Purkinje fibers than in ventricles, and this suggests a role for them in cardiac conduction.

Rate-limiting reactions determining different activation kinetics of Kv1.2 and Kv2.1 channels

To identify the mechanisms underlying the faster activation kinetics in Kv1.2 channels compared to Kv2.1 channels, ionic and gating currents were studied in rat Kv1.2 and human Kv2.1 channels heterologously expressed in mammalian cells. At all voltages the time course of the ionic currents could be described by an initial sigmoidal and a subsequent exponential component and both components were faster in Kv1.2 than in Kv2.1 channels. In Kv1.2 channels, the activation time course was more sigmoid at more depolarized potentials, whereas in Kv2.1 channels it was somewhat less sigmoid at more depolarized potentials. In contrast to the ionic currents, the ON gating currents were similarly fast for both channels. The main portion of the measured ON gating charge moved before the ionic currents were activated. The equivalent gating charge of Kv1.2 ionic currents was twice that of Kv2.1 ionic currents, whereas that of Kv1.2 ON gating currents was smaller than that of Kv2.1 ON gating currents. In conclusion, the different activation kinetics of Kv1.2 and Kv2.1 channels are caused by rate-limiting reactions that follow the charge movement recorded from the gating currents. In Kv1.2 channels, the reaction coupling the voltage-sensor movement to the pore opening contributes to rate limitation in a voltage-dependent fashion, whereas in Kv2.1 channels, activation is additionally rate-limited by a slow reaction in the subunit gating.

Functional expression of GFP-linked human heart sodium channel (hH1) and subcellular localization of the a subunit in HEK293 cells and dog cardiac myocytes

Recent evidence suggests that biosynthesis of the human heart Na+ channel (hH1) protein is rapidly modulated by sympathetic interventions. However, data regarding the intracellular processing of hH1 in vivo are lacking. In this study we sought to establish a model that would allow us to study the subcellular localization of hH1 protein. Such a model could eventually help us to better understand the trafficking of hH1 in vivo and its potential role in cardiac conduction. We labeled the C-terminus of hH1 with the green fluorescent protein (GFP) and compared the expression of this construct (hH1-GFP) and hH1 in transfected HEK293 cells. Fusion of GFP to hH1 did not alter its electrophysiological properties. Confocal microscopy revealed that hH1-GFP was highly expressed in intracellular membrane structures. Immuno-electronmicrographs showed that transfection of hH1-GFP and hH1 induced proliferation of three types of endoplasmic reticulum (ER) membranes to accommodate the heterologously expressed proteins. Labeling with specific markers for the ER and the Golgi apparatus indicated that the intracellular channels are almost exclusively retained within the ER. Immunocytochemical labeling of the Na+ channel in dog cardiomyocytes showed strong fluorescence in the perinuclear region of the cells, a result consistent with our findings in HEK293 cells. We propose that the ER may serve as a reservoir for the cardiac Na+ channels and that the transport from the ER to the Golgi apparatus is among the rate-limiting steps for sarcolemmal expression of Na+ channels.

The beta1 subunit but not the beta2 subunit colocalizes with the human heart Na+ channel (hH1) already within the endoplasmic reticulum

Voltage-dependent Na+ channels are heteromultimers consisting of a pore-forming a subunit and accessory b subunits. In order to provide more insight into the trafficking and assembly of the cardiac Na+ channel complex, we investigated the subcellular localization of the Na+ channel beta1 and beta2 subunits, both in the absence and presence of the human heart Na+ channel (hH1). We fused spectrally distinct variants of the green fluorescent protein (GFP) to hH1 and to the beta1 and beta2 subunit, and expressed the optically labeled b subunits separately or in combination with hH1 in HEK293 cells. In contrast to the predominant localization of hH1 channels within the endoplasmic reticulum (ER), both beta subunits were clearly targeted to the plasma membrane when expressing their cDNAs alone. Upon coexpression of the a subunit, the beta1 subunit was efficiently retained within the ER and found to be colocalized with hH1. In contrast to this, hH1 and the beta2 subunit were not colocalized, i.e., they were detected mainly within the ER and the plasma membrane, respectively. These results indicate that hH1 and the b2 subunit are transported separately to the plasma membrane whereas the hH1/beta1 complex occurs already within the ER, which possibly facilitates trafficking of the channel complex to the plasma membrane.

Amiloride derivatives are potent blockers of KATP channels

In cardiomyocytes sarcolemmal KATP channels open massively when the cytosolic [ATP] drops into the range of tens of micromolar, as during acute ischemia. The diuretic drug amiloride and related derivatives are well established as drugs blocking the Na+/H+- and the Na+/Ca2+-exchange, protecting the ischemic heart. Herein, the blocking action of amiloride and its derivatives 2',4'-dichlorobenzamil (DCB) and 5-(N-ethyl-N-isopropyl)amiloride (EIPA) on KATP channels was tested. In inside-out patches of mouse cardiac myocytes, amiloride, DCB, and EIPA reversibly blocked the KATP channels with the IC50 values 102, 1.80, and 2.14 micromol/l (-80 mV), respectively. Similar IC50 values were obtained in recombinant channels when coexpressing the KIR6.2 subunit with one of the sulfonylurea receptors SUR1 and SUR2A. All three drugs also blocked currents generated by the C-terminus deletion mutant KIR6.2delta26 in the absence of SUR. Amiloride blocked outward currents more effectively than inward currents whereas the block by DCB and EIPA was voltage independent. In cardiomyocytes, also whole-cell IKATP was blocked by the three drugs. In conclusion, amiloride, EIPA, and DCB block the pore-forming KIR6.2 subunit of cardiac KATP channels with higher potency than the Na+/H+- and the Na+/Ca2+-exchange, precluding a specific block of the exchanges under ischemic conditions.

Role of the S2 and S3 segment in determining the activation kinetics in Kv2.1 channels

We constructed chimeras between the rapidly activating Kv1.2 channel and the slowly activating Kv2.1 channel in order to study to what extent sequence differences within the S1-S4 region contribute to the difference in activation kinetics. The channels were expressed in Xenopus oocytes and the currents were measured with a two-microelectrode voltage-clamp technique. Substitution of the S1-S4 region of Kv2.1 subunits by the ones of Kv1.2 resulted in chimeric channels which activated more rapidly than Kv2.1. Furthermore, activation kinetics were nearly voltage-independent in contrast to the pronounced voltage-dependent activation kinetics of both parent channels. Systematic screening of the S1-S4 region by the replacement of smaller protein parts resolved that the main functional changes generated by the S1-S4 substitution were generated by the S2 and the S3 segment. However, the effects of these segments were different: The S3 substitution reduced the effective gating charge and accelerated both a voltage-dependent and a voltage-independent component of the activation time course. In contrast, the S2 substitution accelerated predominantly the voltage-dependent component of the activation time course thereby leaving the effective gating charge unchanged. It is concluded that the S2 and the S3 segment determine the activation kinetics in a specific manner.

Endoscopic ultrasonography of neuroendocrine tumours

Neuroendocrine tumours (NETs) of the upper gastrointestinal tract are mainly located in the pancreas, stomach or duodenum. The aims of preoperative work-up are the localization of primary tumour(s), determination of local tumour invasion, of lymph node metastases and of the hormones secreted by the tumour. Endoscopic ultrasonography (EUS) offers ideal conditions to localize and stage NETs of the foregut. We report our results in localizing and staging NETs of the foregut in 40 patients examined between 1990 and 1997 by EUS, somatostatin receptor scintigraphy (SRS), computed tomography (CT), magnetic resonance imaging (MRI) and transabdominal ultrasound (US). EUS shows the highest sensitivity in localizing insulinomas compared with SRS, US, CT and MRI. US and EUS should be the first-line diagnostics if insulinoma has been proven by a fasting test. Further diagnostic procedures are unnecessary in most cases. Further diagnostics such as CT or MRI to search for distant metastases are necessary in large tumours or local invasive tumours. EUS shows the highest accuracy to detect or exclude pancreatic gastrinomas, but fails to detect extrapancreatic gastrinomas in about 50%. The combination of EUS and SRS gives additional information. First-line diagnostics in gastrinoma patients should be SRS and CT or MRI. If no metastases are detected, EUS should be the next preoperative imaging procedure. In nonfunctional NETs, EUS provides the best information on local tumor invasion and regional lymph node involvement.

Gene regulation in response to overexpression of cytochrome P450 and proliferation of the endoplasmic reticulum in Saccharomyces cerevisiae

(CYP52A4) in Saccharomyces cerevisiae. Using the mRNA differential display technique, six genes were found to be up-regulated: ASN2, MDJ1, YLR194c, YNL208w, YER175, and YGL121c. Genes coding for Dur1.2p, Dal2p, and Sps19p were down-regulated. Two strongly induced genes, which were found to accommodate the peroxisome box (YLR194c) and a 10-bp consensus sequence of genes involved in lipid metabolism (YNL208w) in their promoter regions, were further analyzed with respect to the course of induction, the necessity of the P450 membrane anchor for induction, and the effects of gene disruption on P450Cm2 overexpression. We found that both genes are not essential to overproduce P450Cm2, but their induction was dependent on P450Cm2 membrane integration.

MR imaging-guided biliary drainage in an open low-field system: first clinical experiences

PURPOSE

To test the feasibility of MR imaging (MRI)-guided percutaneous biliary drainages in patients using an open MR-system.

METHODS

6 patients with mechanical cholestasis underwent MRI-guided puncture and catheterization of the biliary system following intervention planning with magnetic resonance cholangiography (MRC) in an open low-field MR system. Data on the number of punctures required, success in establishing external and internal drainage, and total procedure time were compared to those of 6 patients who underwent biliary drainage with fluoroscopic guidance.

RESULTS

MRC facilitated intervention planning in all patients. Near-real-time MR imaging enabled interactive positioning of the devices. The bile ducts were punctured under MRI control in three patients in the first, in two in the second, and in one in the third attempt. MRI-guided puncture was faster than the fluoroscopic procedure. Catheterization for external drainage was successful in all patients. Passing the obstructions was not possible under MRI guidance. The procedure time for MRI-guided catheterization was longer than in the conventional technique.

CONCLUSION

MRI-guidance allows reliable placement of an external biliary drainage in an open low-field MR system.

Detection and prognosis of recurrent gastric cancer--is routine follow-up after gastrectomy worthwhile?

BACKGROUND/AIMS

Although routine follow-up after surgery for gastric cancer is recommended its value after gastrectomy has not been evaluated.

METHODOLOGY

All patients who underwent gastrectomy for gastric cancer entering the routine follow-up program between January 1987 and August 1996 were identified. The patients studied were those with either histologically proven recurrence or those in whom recurrence was highly probable from clinical course. Two groups were compared. The first group comprised the patients whose recurrence was detected by routine follow-up prior to the development of clinical signs (asymptomatic group). The second group consisted of the patients who developed clinical symptoms due to a recurrence that was detected subsequently (symptomatic group). The main parameters were the time until recurrence occurred, the pattern of recurrence, treatment and survival.

RESULTS

Out of 184 patients entering the routine follow-up 135 patients had undergone potentially curative gastrectomy. Sixty-seven patients (49.6%) had recurrences. Only 15 (22.3%) belonged to the asymptomatic group and 52 (77.7%) to the symptomatic one. The time until recurrence occurred was not different between the 2 groups (17.1 vs. 18.0 months). Chemotherapy was performed more frequently in the asymptomatic group and survival was longer (8.4 vs. 5.9 months). This difference was due to the time the patients remained asymptomatic (average 43 months). No effect of either early detection or chemotherapy was seen. In the asymptomatic group distant recurrence was common while recurrence in the symptomatic group was more often local but this difference did not reach statistic significance.

CONCLUSIONS

Routine follow-up after gastrectomy for gastric cancer does not contribute to early detection of gastric cancer recurrence. It has no benefit with respect to treatment and survival of patients with recurrent disease and should therefore be reduced to symptomatic and psychological aftercare.

Esophageal hypermotility associated with intramural pseudodiverticulosis. Primary esophageal disease or epiphenomena?

Esophageal intramural pseudodiverticulosis is a very rare disease of unclear etiology. The clinical picture is characterized by progressive dysphagia. Because of its frequent association with alcohol abuse and subsequent weight loss, it must be differentiated reliably from esophageal carcinoma. The diagnosis is established by the characteristic detection of multiple intramural contrast accumulations in the barium esophagogram. Additional endoscopic and endosonographic confirmation and histological examination are required to exclude a malignant tumor. Moreover, associated diseases are almost always present and should also be diagnosed by pH-metry, cytology, and esophageal manometry. Good and long-lasting therapeutic success can be achieved by bouginage of the stenosis with concomitant treatment of the associated esophageal diseases. Based on two case reports of patients with this disease, we discuss the unusual association with esophageal hypermotility as well as the symptoms, clinical course, therapy, and pathogenesis of the disease.

Misfolded membrane-bound cytochrome P450 activates KAR2 induction through two distinct mechanisms

Using the mRNA differential display technique and Western blot analysis, the present study demonstrates that induction of KAR2 occurs when misfolded membrane-bound cytochrome P450, mutated in its cytosolically exposed domain, is expressed in Saccharomyces cerevisiae. Using various KAR2 promoter constructs in front of the Escherichia coli beta-galactosidase reporter gene, we found a fast and strong induction through the heat shock element (HSE), which was enhanced several fold by its adjacent GC-rich region. Additionally, a less pronounced induction was detected for the UPR element (UPRE). As expected, this response was absent in the ire1 disruptant strain. However, the HSE-mediated induction was enhanced upon disruption of IRE1 suggesting that the HSE pathway can compensate for the lack of a functional UPR pathway. Western blotting confirmed that Kar2p levels were increased to the same extent in the ire1 disruptant and in the non-disruptant strain. Removal of the P450 membrane-spanning region also abolished the UPRE-mediated induction of KAR2 transcription, but the HSE-mediated response remained. The data show for the first time that the transcription of KAR2 is significantly induced in response to a misfolded membrane-bound endoplasmic reticulum protein, and identifies the HSE and UPRE regions as KAR2 promoter elements responding to the misfolded cytosolic P450 domain and to the membrane-integrated mutant P450, respectively.

Null mutation in IRE1 gene inhibits overproduction of microsomal cytochrome P450Alk1 (CYP 52A3) and proliferation of the endoplasmic reticulum in Saccharomyces cerevisiae

Overproduction of microsomal cytochrome P450Alk1 (P450Alk1) of Candida maltosa in Saccharomyces cerevisiae resulted in an extensive proliferation of endoplasmic reticulum (ER) and induction of Kar2p and Pdi1p. The ire1 null mutation severely suppressed ER proliferation, reduced the level of functional P450Alk1, and showed no induction of these ER chaperones, suggesting that the function of Ire1p is required for ER proliferation upon the overproduction of P450Alk1. Cerulenin, a potent inhibitor of lipid biosynthesis, also induced these chaperones in an Ire1p-dependent manner and limited the production of functional P450Alk1. These results imply that Ire1p may function to restore the balance between membrane proteins and lipids of the ER when the ER is relatively overcrowded by membrane proteins.

[Value of magnetic resonance tomography in preoperative staging of stomach carcinoma]

The value of MRI as a preoperative staging procedure in stomach carcinomas compared to CT and endosonography was examined in a prospective study and correlated with the pathohistological results. MRI showed better correlation with the pathohistological evaluation at the T3, T4, N and M stage than the other two test procedures. MRI is thus a suitable staging procedure for stomach carcinomas.

Oxygenation cascade in conversion of n-alkanes to alpha,omega-dioic acids catalyzed by cytochrome P450 52A3

Purified recombinant cytochrome P450 52A3 and the corresponding NADPH-cytochrome P450 reductase from the alkane-assimilating yeast Candida maltosa were reconstituted into an active alkane monooxygenase system. Besides the primary product, 1-hexadecanol, the conversion of hexadecane yielded up to five additional metabolites, which were identified by gas chromatography-electron impact mass spectrometry as hexadecanal, hexadecanoic acid, 1, 16-hexadecanediol, 16-hydroxyhexadecanoic acid, and 1, 16-hexadecanedioic acid. As shown by substrate binding studies, the final product 1,16-hexadecanedioic acid acts as a competitive inhibitor of n-alkane binding and may be important for the metabolic regulation of the P450 activity. Kinetic studies of the individual sequential reactions revealed high Vmax values for the conversion of hexadecane, 1-hexadecanol, and hexadecanal (27, 23, and 69 min-1, respectively), whereas the oxidation of hexadecanoic acid, 1, 16-hexadecanediol, and 16-hydroxyhexadecanoic acid occurred at significantly lower rates (9, 9, and 5 min-1, respectively). 1-Hexadecanol was found to be the main branch point between mono- and diterminal oxidation. Taken together with data on the incorporation of 18O2-derived oxygen into the hexadecane oxidation products, the present study demonstrates that a single P450 form is able to efficiently catalyze a cascade of sequential mono- and diterminal monooxygenation reactions from n-alkanes to alpha, omega-dioic acids with high regioselectivity.

Relation between evolutionary distance and enzymatic properties among the members of the CYP52A subfamily of Candida maltosa

The CYP52A subfamily of the alkane-assimilating yeast Candida maltosa consists of six structurally related isoforms. Four of them (CYP52A3, 4, 5, and 9) are strongly induced by alkanes and play an important role for the conversion of various alkanes and fatty acids. Taking advantage of a homologous overexpression system, we found in the present study that both of the two other CYP52A forms, CYP52A10 and CYP52A11, represent specialists for the hydroxylation of lauric acid suggesting their preference for short-chain fatty acids. At the same time, they hydroxylated palmitic acid only moderately and failed to convert hexadecane. Based on the now completed knowledge about the principal substrate specificities of all members of the CYP52A subfamily of C. maltosa, it became apparent that evolutionarily more distantly related P450 forms developed either to alkane or to fatty acid hydroxylases, whereas P450 forms which retained the ability to convert both types of substrates were also found to be evolutionarily related to both alkane and fatty acid hydroxylases.

Mutual conversion of fatty-acid substrate specificity by a single amino-acid exchange at position 527 in P-450Cm2 and P-450Alk3A

The two eukaryotic fatty-acid hydroxylases P-450Cm2 and P-450Alk3A, which represent CYP52A4 variants naturally occurring in the yeast Candida maltosa, were characterized with respect to their substrate specificity. Whereas P-450Cm2 was found to catalyse lauric acid omega-hydroxylation with greater efficiency, P-450Alk3A had higher palmitic acid turnover numbers compared to P-450Cm2, resulting in ratios of lauric acid to palmitic acid turnover rates of nearly 11 and 3 for P-450Cm2 and P-450Alk3A, respectively. As shown by means of chimeric enzymes and site-directed mutagenesis, the key residue determining these differences in substrate specificity was found to be a single amino acid at position 527. Interestingly, the mutual exchange of valine (P-450Cm2) and leucine (P-450Alk3A) led to a direct transposition of specificity, suggesting that amino acids at this site may determine the efficiency of fatty-acid hydroxylation relatively independently of other active-site residues. This was further supported by the finding that P-450Cm2 and P-450Alk3A with methionine at position 527 displayed almost identical hydroxylation activities. Moreover, methionine to leucine substitutions at the corresponding alignment position in P-450Cm1 (CYP52A3), P-450Alk2A (CYP52A5) and P-450Alk5A (CYP52A9) altered the fatty-acid specificity of these enzymes. In comparison to the structure of the bacterial P-450BM3 (CYP102), we propose that the amino acid at position 527 may serve to close the substrate-binding pocket near to the haem in the fatty-acid-omega-hydroxylating P-450 of the CYP52 family.

[Is routine tumor after-care after gastrectomy sensible?]

Only 22.3% of patients with recurrence after potentially curative gastrectomy are discovered in asymptomatic stages. Their prognosis is not different from those with symptomatic recurrence. Routine follow-up after gastrectomy can be abandoned.

Isozyme function of n-alkane-inducible cytochromes P450 in Candida maltosa revealed by sequential gene disruption

An n-alkane-assimilating yeast Candida maltosa contains multiple n-alkane-inducible forms of cytochromes P450 (P450alk), which can be assumed to catalyze terminal hydroxylation of n-alkanes in the assimilation pathway. Eight structurally related P450alk genes have been identified. In the present study, the function of four major isoforms of P450alk (encoded by ALK1, ALK2, ALK3, and ALK5 genes) was investigated by sequential gene disruption. Auxotrophic markers used for the selection of disrupted strains were regenerated repeatedly through either mitotic recombination between heterozygous alleles of the diploid genome or directed deletion of the marker gene, to allow sequential gene disruptions within a single strain. The strain depleted of all four isoforms could not utilize n-alkanes for growth, providing direct evidence that P450alk is essential for n-alkane assimilation. Growth properties of a series of intermediate disrupted strains, plasmid-based complementation, and enzyme assays after heterologous expression of single isoforms revealed (i) that each of the four individual isoforms is alone sufficient to allow growth on long chain n-alkane; (ii) that the ALK1-encoding isoform is the most versatile and efficient P450alk form, considering both its enzymatic activity and its ability to confer growth on n-alkanes of different chain length; and (iii) that the ALK5-encoding isoform exhibits a rather narrow substrate specificity and thus cannot support the utilization of short chain n-alkanes.

Endoscopic sclerotherapy with fibrin glue as compared with polidocanol to prevent early esophageal variceal rebleeding

BACKGROUND/AIMS

Endoscopic sclerotherapy is of proven benefit for patients after esophageal variceal bleeding, but is associated with substantial local and systemic complications. Since fibrin glue is a promising agent for endoscopic sclerotherapy of esophageal varices, we compared its safety and efficacy in patients after esophageal variceal bleeding.

PATIENTS AND METHODS

In a randomized, controlled trial, 36 patients with an acute episode of variceal bleeding were endoscopically treated with either polidocanol (18 patients) or fibrin glue (18 patients) by intravariceal injections within 12 h of admission. Tissue compatibility, incidence of various complications, episodes of rebleeding and overall survival rates were investigated.

RESULTS

Rebleeding, especially from enrollment to day 28, was less common in the fibrin group (p=0.046), and all patients treated with fibrin glue survived for more than 28 days, whereas five patients treated with polidocanol died within this period. The incidence of sclerotherapy-induced ulcers was significantly lower in the fibrin group than in the polidocanol group (p=0.001), and major complications such as perforation or ulcer bleeding were observed only in the polidocanol group. There were no complications in any group due to activation of systemic coagulation, fibrinolysis or clinically relevant pulmonary embolization.

CONCLUSIONS

We conclude that fibrin glue is an efficient and safe agent for endoscopic sclerotherapy of bleeding esophageal varices, especially in the immediate posthemorrhagic period.

[MR cholangiopancreatography using an open low field system of 0.2 tesla: early clinical results compared with a high field system (1.5 tesla) and ERCP]

AIM

To evaluate MR cholangio-pancreatography (MRCP) using an open low magnetic field apparatus in normals and in patients with mechanical cholestasis.

METHODS

MRCP was performed on five normals and on 30 patients, using both an 0.2 Tesla and 1.5 Tesla apparatus. With the low field system, rapid acquisition by relaxation enhancement was used, for the high field system, half Fourier acquisition single shot turbo spin-echo sequences were used. In all patients, sonography and ERCP or PTC was performed; 23 underwent surgery.

RESULTS

In all normals it was possible to show the bile duct, hepatic duct, gall bladder and intrahepatic ducts of the first order. Using the high field system, second order ducts could be shown and sometimes third order ducts. In the patients, MRCP, using either system, demonstrated all 21 obstructive sites due to tumours or stenoses. Stones were shown in 69% by the low field system and in 88% by the high field system.

CONCLUSION

MRCP can be successfully carried out using the low field system. In the presence of mechanical cholestasis, image quality is adequate for the localisation of stenoses and occlusions, and, using an open magnet, is suitable for planning further intervention.

[Intramural pseudodiverticulosis of the esophagus]

Esophageal intramural pseudodiverticulosis is a rare benign condition with the cardinal symptom of dysphagia mostly due to inflammatory strictures. The disease frequently develops in connection with alcohol abuse and esophageal reflux, candidiasis or motility disorders. Characteristic is the radiological visualization of intramural saccular contrast accumulations. We report on five patients with esophageal pseudodiverticulosis endoscopically diagnosed at our hospital within a period of five years. Four of these patients underwent extensive investigations for additional esophageal conditions: Histological/cytological examinations, manometry, pH-metry and endoscopic ultrasonography. These four patients had a pathological reflux with marked esophagitis and inflammatory strictures. We achieved long-lasting therapeutic results with complete relief by bougienage and reflux therapy with additional candidiasis treatment in two and motility treatment in one patient each. The detailed discussion deals with the clinical aspects, characteristics, therapy and pathogenesis.

A 7-year-old child with primary tumour localisation in the distal duodenum--new imaging procedures for an improved diagnosis

Duodenal gastrinomas in childhood are extremely rare and often missed at first medical consultation. We report on a 7-year-old child with sporadic gastrinoma of primary localisation in the distal duodenum. Small metastases in the liver and regional nodes were detected pre-operatively by somatostatin receptor scintigraphy (SRS) but not by other conventional imaging procedures. Diagnostic procedures include pre-operative SRS, endoscopic ultrasound and intra-operative endoscopic transillumination.

CONCLUSION

Gastrinomas are rare abdominal tumours in childhood. Pre-operative tumour-specific diagnosis is possible by 111indium pentreotide SRS.

Protein quality--a determinant of the intracellular fate of membrane-bound cytochromes P450 in yeast

To elucidate mechanisms determining the intracellular localization of cytochromes P450, authentic and mutant cytochromes P450 52A4 (P450Cm2) and P450 52A5 (P450Alk2A) were heterologously expressed in Saccharomyces cerevisiae and the ultrastructure of the respective transformants was investigated by means of immunoelectron microscopy. As a result, overproduction of both wild-type P450 forms resulted in a massive proliferation of tubular membrane structures distributed over the whole cytoplasm. In contrast, all mutant P450Cm2 and Alk2A forms tested were mainly localized within stacks of paired membranes which often occurred in close vicinity to the nucleus. As found by serial sectioning of a single cell, these stacked membranes bearing the mutant P450 actually represented plates of consecutive membranes arranged one upon the other. A tubular network of endoplasmic reticulum membranes as observed after expression of the wild-type proteins could not be detected. Generally, the kind of mutation introduced into the P450 forms did not influence the morphology of the induced membranes. Even single amino acid exchanges in the cytosolic domain caused the formation of membrane stacks. The common feature of all mutant P450 forms causing the formation of stacked membranes was, however, their lower protein stability after heterologous expression in the S. cerevisiae host cells, compared to the stability of the authentic cytochromes P450. Furthermore, the proliferated membranes containing the different P450 forms were characterized by means of subcellular fractionation experiments. Using this approach, clear differences in the distribution of spectrally active and inactive P450 molecules were found. The results obtained suggest the presence of an intracellular sorting mechanism based on the protein quality, which finally leads to the differences in the intracellular distribution of wild-type and mutant cytochromes P450.

[Value of endoscopic ultrasound examination of the mediastinum in Hodgkin's and non-Hodgkin's lymphomas]

AIM

The applicability of ultrasound for diagnosing mediastinal diseases is limited by the surrounding thorax containing air and bone, permitting only restricted echo windows. Transoesophageal endoscopic ultrasound circumvents this problem and provides good visualisation of nearly all parts of the mediastinum. We evaluated the value of endoscopic ultrasonography for mediastinal staging of Hodgkin's and non-Hodgkin lymphoma patients.

PATIENTS AND METHODS

From August 1994 to July 1995 36 Hodgkin's and non-Hodgkin lymphoma patients underwent clinical staging and were endosonographically examined for mediastinal involvement. CT in the spiral technique was used as the reference.

RESULTS

In assessing mediastinal involvement, endoscopic ultrasound revealed a sensitivity of 96% and a specificity of 75%. There were limitations in the right paratracheal region and the area lateral to the aortic arch.

CONCLUSION

Endoscopic ultrasound is a highly valuable imaging procedure for diagnosing mediastinal spread of malignant lymphomas and has interesting potentials in assessing the clinical course during therapy.

[Endoscopic ultrasound of pathological mediastinal findings]

INTRODUCTION

Mediastinal diseases are mostly diagnosed by CT and MRI. The applicability of ultrasound is limited by the surrounding air- and bone-containing thorax, which permits only restricted echo windows. Transesophageal endoscopic ultrasonography circumvents this problem and ensures visualization of parts of the mediastinum.

PATIENTS AND METHODS

We report our results in 38 patients with pathological mediastinal findings who were examined by endoscopic ultrasound between 1988 and 1993. The diagnoses were established by imaging and/or histological procedures.

RESULTS

The following mediastinal diseases were diagnosed in 38 patients: aberrant right subclavian artery (n = 3), right aortic arch (n = 1), aortic aneurysm (n = 6), cysts (n = 4), retrosternal struma (n = 3), mediastinal lymph node tuberculosis (n = 1), Hodgkin's/non-Hodgkin's lymphomas (n = 11), lymph node involvement in bronchogenic carcinoma (n = 8), mediastinal inflammatory fibrosarcoma (n = 1). Altogether, 37/38 pathological findings were demonstrated endosonographically.

CONCLUSIONS

The results in this small group of patients with pathological mediastinal findings show that endoscopic ultrasound can give additional information to conventional imaging methods. A prospective comparative study is necessary to evaluate this procedure in comparison to the established imaging techniques.

Endoscopic ultrasonography and somatostatin receptor scintigraphy in the preoperative localisation of insulinomas and gastrinomas

BACKGROUND

Endoscopic ultrasonography (EUS) and somatostatin receptor scintigraphy (SRS) can detect a high percentage of gastroenteropancreatic neuroendocrine tumours especially in the upper gastrointestinal tract. The ability of these procedures to localise primary tumour lesions and metastases of gastrinomas and insulinomas was evaluated in comparison with transabdominal ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI).

PATIENTS AND METHODS

In a prospective trial, patients with gastrinomas (n = 10) and insulinomas (n = 10) diagnosed by clinical signs and laboratory tests were assessed by EUS, SRS, US, CT and MRI.

RESULTS

In 10 patients with gastrinoma and 10 patients with insulinoma, a total of 14 separate primary tumour lesions were histologically confirmed for each of the tumour entities. The mean diameter was 2.1 cm for gastrinomas and 1.5 cm for insulinomas. All insulinomas and nine gastrinoma lesions were located in the pancreas. Three gastrinomas were found in the duodenal wall, one in a periduodenal lymph node, and one in the liver, For gastrinomas, sensitivities were 79% with EUS, 86% with SRS and 29% with CT, US, and MRI. For insulinomas, sensitivities were 93% with EUS, 14% with SRS, 21% with CT and 7% with US and MRI.

CONCLUSIONS

EUS is of high value for localising primary lesions of both tumour entities. SRS is a very sensitive procedure for diagnosing of gastrinomas but not insulinomas. CT, US and MRI are primarily useful for visualising metastases.

The CYP52 multigene family of Candida maltosa encodes functionally diverse n-alkane-inducible cytochromes P450

The n-alkane-assimilating yeast Candida maltosa contains several structurally related cytochromes P450 (P450) encoded by the CYP52 multigene family, which are inducible by various long-chain hydrocarbons and fatty acids and which are responsible for the initial hydroxylation steps in the metabolism of these substrates. In the present work, the four major n-alkane-inducible C. maltosa P450 forms; CYP52A3, CYP52A4, CYP52A5, and CYP52A9, were enzymatically characterized, taking advantage of heterologous P450/reductase coexpression in Saccharomyces cerevisiae. Testing various alkanes and fatty acids, distinct preferences of the individual P450 forms concerning substrate class and chain length were detected, thus providing new insight into the functional diversity of the C. maltosa CYP52 family. Moreover, the results obtained emphasize these structurally related enzymes as a powerful tool for future studies on P450 structure-function relationships.

Characterization of the n-alkane and fatty acid hydroxylating cytochrome P450 forms 52A3 and 52A4

Two enzymes, P450 52A3 (P450Cm1) and 52A4 (P450Cm2), the genes of which belong to the CYP52 multigene family occurring in the alkane-assimilating yeast Candida maltosa, have been characterized biochemically and compared in terms of their substrate specificities. For this purpose, both the p450 proteins and the corresponding C. maltosa NADPH-cytochrome P450 reductase were separately produced by expressing their cDNAs in Saccharomyces cerevisiae, purified, and reconstituted to active monooxygenase systems. Starting from microsomal fractions with a specific content of 0.75 nmol P450Cm1, 0.34 nmol P450Cm2, and 10.5 units reductase per milligram of protein, respectively, each individual recombinant protein was purified to homogeneity. P450 substrate difference spectra indicated strong type I spectral changes and high-affinity binding of n-hexadecane (Ks= 26 micron) and n-octadecane (Ks = 27 microM) to P450Cm1, whereas preferential binding to P450Cm2 was observed using lauric acid (Ks = 127 microM) and myristic acid (Ks = 134 microM) as substrates. These substrate selectivities were further substantiated by kinetic parameters, determined for n-alkane and fatty acid hydroxylation in a reconstituted system, which was composed of the purified components and phospholipid, as well as in microsomes obtained after coexpressing each of the P450 proteins with the reductase. The highest catalytic activities within the reconstituted system were measured for n-hexadecane hydroxylation to 1-hexadecanol by P450Cm1 (Vmax = 27 microM x min-1, Km = 54 microM) and oxidation of lauric acid to 16-hydroxylauric acid by P450Cm2 (Vmax = 30 microM x min-1, Km = 61 microM). We conclude that P450Cm1 and P450Cm2 exhibit overlapping but distinct substrate specificities due to different chain-length dependencies and preferences for either n-alkanes or fatty acids.

[Gastric hamartoma and thyroid gland carcinoma with follicular and neuroendocrine differentiation in Cowden syndrome]

A 40-year old male patient presented with a history of subtotal strumectomy, excision of multiple cutaneous lesions at the upper trunk and gastrointestinal polyposis of unknown origin. The patient was admitted for weight loss and intermittent diarrhea. Physical examination revealed craniomegaly, papillomatosis of the oral mucosa and epigastric tenderness. Endoscopically, multiple polyps were seen in the stomach, the duodenum, the terminal ileum, the distal colon and the rectum. Histologically, these lesions were classified as hamartomatous and hyperplastic polyps. In the punctate of the relapsed nodular goitre, neoplastic follicular cells were found. These findings led to the diagnosis of Cowden's disease. A complete thyroidectomy was performed. The histology verified a follicular thyroid carcinoma and showed a combined expression of thyroglobulin and of the neuroendocrine marker synaptophysin (appr. 50% of all tumor cells). Chromogranin A (a neuroendocrine tumor marker) was also elevated in the serum of the patient. Postoperatively, a radioiodine therapy was performed and the clinical condition of the patient has improved ever since. The presented case of Cowden's disease is the first male patient with thyroid carcinoma. Early consideration of Cowden's disease is substantial as multiple malignant neoplasms may occur in this disorder in increased incidence.

In vivo reconstitution of highly active Candida maltosa cytochrome P450 monooxygenase systems in inducible membranes of Saccharomyces cerevisiae

To establish a system for functional characterization of individual Candida maltosa cytochrome P450 monooxygenases, the NADPH-cytochrome P450 reductase from this yeast species was co-expressed in Saccharomyces cerevisiae with each of the following cytochrome P450 forms; P450Cm1 (CYP52 A3), P450Cm2 (CYP52 A4), and P450AlK2A (CYP52 A5). For this purpose, a multicopy plasmid was constructed that contained two independent expression units controlled by the galactose-inducible GAL10 promoter. As shown by spectral and immunological methods, large amounts of the desired monooxygenase components could be simultaneously produced in the respective S. cerevisiae transformants. It was important, however, to adjust semi-anaerobic cultivation conditions during induction by galactose to minimize a mutual impairment of cytochrome P450 and NADPH-cytochrome P450 reductase formation. Compared to the specific cellular content of the host-own enzyme, a 75- to 100-fold overproduction of the reductase component was obtained resulting in P450/reductase molar ratios of about 1:3 in the microsomal fractions prepared from the co-expression strains. At the same time, the rates of cytochrome P450-dependent lauric acid hydroxylation increased more than 10-fold, showing a proper reconstitution of the C. maltosa monooxygenase systems in S. cerevisiae. Using intact cells, an efficient biotransformation of lauric acid to omega-hydroxylauric acid and dodecanedioic acid was found. S. cerevisiae cells coexpressing cytochrome P450 and NADPH-cytochrome P450 reductase were characterized by a marked proliferation of the endoplasmic reticulum. Immunoelectron microscopy revealed a colocalization of the monooxygenase components produced to these newly formed membrane structures.

Spheric duodenal duplication in a 13-year-old child

Duodenal duplications are rare. Modern imaging procedures demonstrate the relation of the duplication to the duodenum and the adjacent organs. Thus the surgical procedure can be selected preoperatively. Endoscopic ultrasound is an excellent technique for visualizing a duodenal duplication. A cystic duodenal duplication measuring 6 cm in diameter was resected in a 13-year-old boy.