Hepatobiliary long-term consequences of COVID-19: dramatically increased rate of secondary sclerosing cholangitis in critically ill COVID-19 patients

BACKGROUND

Increasing evidence suggests that secondary sclerosing cholangitis (SSC), which can lead to cirrhosis or liver failure, may be a hepatobiliary long-term complication of COVID-19. The aim of this study was to estimate the frequency and outcome of this COVID-19 sequela and to identify possible risk factors.

METHODS

This observational study, conducted at University Hospital Charité Berlin and Unfallkrankenhaus Berlin, Germany, involved hospitalized patients with COVID-19 pneumonia, including 1082 ventilated COVID-19 patients. We compared COVID-19 patients who developed SSC with a COVID-19 control group by univariate and multivariate analyses.

RESULTS

SSC occurrence after COVID-19 was observed exclusively in critically ill patients with invasive ventilation, albeit with extreme clustering among them. One in every 43 invasively ventilated COVID-19 patients developed this complication. Risk factors preceding the development of secondary sclerosing cholangitis in critically ill COVID-19 patients (SSC-CIP) were signs of systemic reduced blood oxygen supply (e.g., low PaO2/FiO2, ischemic organ infarctions), multi-organ failure (high SOFA score) at admission, high fibrinogen levels and intravenous ketamine use. Multivariate analysis confirmed fibrinogen and increased plasma lactate dehydrogenase as independent risk factors associated with cholangiopathy onset. The 1-year transplant-free survival rate of COVID-19-associated SSC-CIP was 40%.

CONCLUSIONS

COVID-19 causes SSC-CIP in a substantial proportion of critically ill patients. SSC-CIP most likely develops due to severe tissue hypoxia and fibrinogen-associated circulatory disturbances. A significant increase of patients with SSC-CIP is to be expected in the post-COVID era.

6 Monate Zulassung von Kaftrio® in Deutschland – erste Erfahrungen aus dem „wahren Leben“ von Menschen mit CF

Hintergrund

Mit der Weiterentwicklung der „Cystic-fibrosis-transmembrane-conductance-regulator“(CFTR)-Modulatoren und der Zulassung von Kaftrio® (Elexacaftor, Tezacaftor, Ivacaftor) für einen Großteil der Menschen mit CF steht neben der etablierten symptomatischen Therapie nun eine weitere vielversprechende Therapieoption zur kausalen Behandlung der CF zur Verfügung.

Fragestellung

Ziel der hier vorliegenden Arbeit ist es, erste Effekte der Kaftrio®-Therapie auf den klinischen Phänotyp von Menschen mit CF 6 Monate nach der Zulassung zu untersuchen sowie die Ergebnisse in den Kontext neuer daraus resultierender Fragestellungen für die zukünftige Behandlung von CF-Patient*innen zu stellen.

Material und Methoden

Im Rahmen dieser Arbeit wurden anonymisiert klinische Daten (FEV1, Body-Mass-Index, HbA1c, Schweiß-Chlorid-Konzentration, Leberwerte) von 56 an der Uniklinik Köln betreuten Patient*innen retrospektiv ausgewertet, die die Voraussetzungen für eine Behandlung mit Kaftrio® erfüllt haben (Alter >12 Jahre, F508del homozygot oder heterozygot) und die mindestens >4 Wochen Kaftrio® eingenommen haben. Unterschiede zwischen den Gruppen wurden mithilfe des „Paired-t“-Tests berechnet. Ein p-Wert <0,05 wurde als statistisch signifikant gewertet.

Ergebnisse

In der untersuchten Kohorte konnte unter Kaftrio®-Therapie ein durchschnittlicher Anstieg der Einsekundenkapazität (FEV1-Werte in % des Sollwertes) um 11,3 % nachgewiesen werden. Ferner kam es unter Kaftrio® zu einem signifikanten Anstieg des Body-Mass Index (BMI) (+0,89 kg/m2), einer deutlichen Reduktion der Schweiß-Chlorid-Konzentration um durchschnittlich 58,8 mmol/l sowie zu einem Anstieg der Leberwerte.

Diskussion

Unsere retrospektive Datenerhebung bestätigt die aus den Zulassungsstudien beschriebenen positiven Effekte der Kaftrio®-Therapie auf den klinischen Phänotyp der Menschen mit CF. Mit der Besserung der Lungenfunktion, des Ernährungsstatus und der daraus resultierenden gesteigerten Lebenserwartung wird neben der Reevaluation bisheriger Behandlungsstandards der Fokus zukünftig auch auf dem Erhalt der Lebensqualität durch frühzeitige Diagnostik und effiziente Therapie möglicher Begleiterkrankungen liegen müssen.

Use of Hemoadsorption in Patients With Severe Intoxication Requiring Extracorporeal Cardiopulmonary Support-A Case Series

Drugs intoxications often lead to severe vasoplegia and cardiogenic shock, and VA-ECMO represents a viable therapy option. However, as cardiopulmonary support is not contributing to the removal of the causal agent from the blood, detoxification by a new hemoadsorption device (CytoSorb) could represent a potential therapeutic tool due to its highly efficient elimination capacity of endogenous but also exogenous hydrophobic substances for which otherwise no effective antidote exist. In this case series, four anecdotal cases of acute intoxications requiring VA-ECMO support used as extracorporeal cardiopulmonary resuscitation after intoxication-induced out-of-hospital cardiac arrest (OHCA) are presented, who were additionally treated with CytoSorb hemoadsorption in combination with renal replacement therapy. Combined treatment was associated with a considerable decrease in plasma levels of the overdosed drugs. Additionally, the combination of applied techniques was safe, practical, and technically feasible with no adverse or any device-related side effects documented during or after the treatment sessions. Based on the reported dramatic decline in drug levels during treatment, that fits in the device's characteristics, we strongly suggest to further investigate the potentially lifesaving role of CytoSorb therapy in patients with acute intoxications requiring multiple organ support techniques.

Critical Illness and Systemic Inflammation Are Key Risk Factors of Severe Acute Kidney Injury in Patients With COVID-19

INTRODUCTION

Acute kidney injury (AKI) is an important complication in COVID-19, but its precise etiology has not fully been elucidated. Insights into AKI mechanisms may be provided by analyzing the temporal associations of clinical parameters reflecting disease processes and AKI development.

METHODS

We performed an observational cohort study of 223 consecutive COVID-19 patients treated at 3 sites of a tertiary care referral center to describe the evolvement of severe AKI (Kidney Disease: Improving Global Outcomes stage 3) and identify conditions promoting its development. Descriptive statistics and explanatory multivariable Cox regression modeling with clinical parameters as time-varying covariates were used to identify risk factors of severe AKI.

RESULTS

Severe AKI developed in 70 of 223 patients (31%) with COVID-19, of which 95.7% required kidney replacement therapy. Patients with severe AKI were older, predominantly male, had more comorbidities, and displayed excess mortality. Severe AKI occurred exclusively in intensive care unit patients, and 97.3% of the patients developing severe AKI had respiratory failure. Mechanical ventilation, vasopressor therapy, and inflammatory markers (serum procalcitonin levels and leucocyte count) were independent time-varying risk factors of severe AKI. Increasing inflammatory markers displayed a close temporal association with the development of severe AKI. Sensitivity analysis on risk factors of AKI stage 2 and 3 combined confirmed these findings.

CONCLUSION

Severe AKI in COVID-19 was tightly coupled with critical illness and systemic inflammation and was not observed in milder disease courses. These findings suggest that traditional systemic AKI mechanisms rather than kidney-specific processes contribute to severe AKI in COVID-19.

Fallstricke in der Dermatologie: Hautläsionen am Shuntarm einer Dialysepatientin durch Steal-Phänomen

Wir berichten über eine 78-jährige dialysepflichtige Patientin, welche sich mit stark schmerzhaften Nekrosen distal eines Dialyseshunts vorstellte und bei der abschließend ein Steal-Phänomen diagnostiziert wurde. Beim Steal-Syndrom handelt es sich um eine seltene Komplikation eines Gefäßshunts durch Minderperfusion der Extremität distal der AV-Anastomose. Diabetiker sind aufgrund des höheren peripheren Gefäßwiderstandes und der Mikroangiopathie eher gefährdet, ein Steal-Syndrom nach Shuntanlage zu entwickeln. Der vorgestellte Fall soll verdeutlichen, dass das Steal-Syndrom dringlich in die differenzialdiagnostischen Überlegungen bei kutanen Nekrosen am Shuntarm einzuschließen ist und die Patienten schnellstmöglich gefäßchirurgisch vorzustellen sind, um einen Zeitverlust bis zur therapeutischen Intervention mit der Gefahr des irreversiblen Gewebsverlust und damit verbunden ggf. konsekutiv erforderliche Amputationen zu vermeiden.

The nucleolus functions as a phase-separated protein quality control compartment

The nuclear proteome is rich in stress-sensitive proteins, which suggests that effective protein quality control mechanisms are in place to ensure conformational maintenance. We investigated the role of the nucleolus in this process. In mammalian tissue culture cells under stress conditions, misfolded proteins entered the granular component (GC) phase of the nucleolus. Transient associations with nucleolar proteins such as NPM1 conferred low mobility to misfolded proteins within the liquid-like GC phase, avoiding irreversible aggregation. Refolding and extraction of proteins from the nucleolus during recovery from stress was Hsp70-dependent. The capacity of the nucleolus to store misfolded proteins was limited, and prolonged stress led to a transition of the nucleolar matrix from liquid-like to solid, with loss of reversibility and dysfunction in quality control. Thus, we suggest that the nucleolus has chaperone-like properties and can promote nuclear protein maintenance under stress.

Graph-Based Molecular Alignment (GMA)

We describe a combined 2D/3D approach for the superposition of flexible chemical structures, which is based on recent progress in the efficient identification of common subgraphs and a gradient-based torsion space optimization algorithm. The simplicity of the approach is reflected in its generality and computational efficiency: the suggested approach neither requires precalculated statistics on the conformations of the molecules nor does it make simplifying assumptions on the topology of the molecules being compared. Furthermore, graph-based molecular alignment produces alignments that are consistent with the chemistry of the molecules as well as their general structure, as it depends on both the local connectivities between atoms and the overall topology of the molecules. We validate this approach on benchmark sets taken from the literature and show that it leads to good results compared to computationally and algorithmically more involved methods. The results suggest that, for most practical purposes, graph-based molecular alignment is a viable alternative to molecular field alignment with respect to structural superposition and leads to structures of comparable quality in a fraction of the time.

[Anemia and erythropoietin in critically ill patients]

The transfusion of red blood cells is still associated with possible adverse effects and a residual risk of transmission of viral and nonviral diseases. In addition, there is an increasing shortage of blood supply worldwide. These two facts together with the success experienced in the treatment of various types of anemia with recombinant human EPO, have recently led to an increasing interest in the anemia of critically ill patients. As in the anemia of chronic diseases there are several reasons that contribute to the development of anemia in patients on intensive care units: pre-existing anemia, blood loss, reduced red cell life span, impaired iron availability and a direct inhibition of erythropoiesis by inflammatory cytokines. The implications of anemia for the progression and prognosis of critical illness are still unclear and the optimal treatment, including optimal "transfusion triggers" remains controversial. Recombinant human EPO has been proven to be effective in ameliorating the anemia of critical illness in several pilot studies and is currently being tested in larger trials.

Hydrolysis of pectins with different degrees and patterns of methylation by the endopolygalacturonase of Fusarium moniliforme

The mode of action of the endopolygalacturonase from Fusarium moniliforme was studied towards a series of pectins with different amounts and distribution patterns of methyl-ester groups. The enzyme hydrolysed the linkages between two galacturonic acid residues according to a multi-chain attack mechanism, at least at the early stage of the reaction. The final percentage of hydrolysis decreased with increasing the degree of methylation. The distribution pattern of the methyl groups affected the rate of hydrolysis as well as the final percentage of hydrolysis, a blockwise distribution being more favourable than a random one. The final products, as analysed by mass spectrometry, included methyl-esterified oligogalacturonates. The detailed analysis of the structure of the oligomers showed that the enzyme was able to accommodate methylated galacturonic acid in its active site, but that methyl-esterification negatively affected the affinity of the enzyme.

A GRASP55-rab2 effector complex linking Golgi structure to membrane traffic

Membrane traffic between the endoplasmic reticulum (ER) and Golgi apparatus and through the Golgi apparatus is a highly regulated process controlled by members of the rab GTPase family. The GTP form of rab1 regulates ER to Golgi transport by interaction with the vesicle tethering factor p115 and the cis-Golgi matrix protein GM130, also part of a complex with GRASP65 important for the organization of cis-Golgi cisternae. Here, we find that a novel coiled-coil protein golgin-45 interacts with the medial-Golgi matrix protein GRASP55 and the GTP form of rab2 but not other Golgi rab proteins. Depletion of golgin-45 disrupts the Golgi apparatus and causes a block in secretory protein transport. These results demonstrate that GRASP55 and golgin-45 form a rab2 effector complex on medial-Golgi essential for normal protein transport and Golgi structure.

Golgi matrix proteins interact with p24 cargo receptors and aid their efficient retention in the Golgi apparatus

The Golgi apparatus is a highly complex organelle comprised of a stack of cisternal membranes on the secretory pathway from the ER to the cell surface. This structure is maintained by an exoskeleton or Golgi matrix constructed from a family of coiled-coil proteins, the golgins, and other peripheral membrane components such as GRASP55 and GRASP65. Here we find that TMP21, p24a, and gp25L, members of the p24 cargo receptor family, are present in complexes with GRASP55 and GRASP65 in vivo. GRASPs interact directly with the cytoplasmic domains of specific p24 cargo receptors depending on their oligomeric state, and mutation of the GRASP binding site in the cytoplasmic tail of one of these, p24a, results in it being transported to the cell surface. These results suggest that one function of the Golgi matrix is to aid efficient retention or sequestration of p24 cargo receptors and other membrane proteins in the Golgi apparatus.

Study of the mode of action of endopolygalacturonase from Fusarium moniliforme

One endopolygalacturonase from Fusarium moniliforme was purified from the culture broth of a transformed strain of Saccharomyces cerevisiae. Its kinetic parameters and mode of action were studied on galacturonic acid oligomers and homogalacturonan. The dimer was not a substrate for the enzyme. The enzyme was shown to follow Michaelis-Menten behaviour towards the other substrates tested. Affinity and maximum rate of hydrolysis increased with increasing chain length, up to the hexamer or heptamer, for which V(max) was in the same range as with homogalacturonan. The enzyme was demonstrated to have a multi-chain attack mode of action and its active site included five subsites ranging from -3 to +2. The final products of hydrolysis of homogalacturonan were the monomer and the dimer of galacturonic acid.

Negative and positive ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and positive ion nano-electrospray ionization quadrupole ion trap mass spectrometry of peptidoglycan fragments isolated from various Bacillus species

A general approach for the detailed characterization of sodium borohydride-reduced peptidoglycan fragments (syn. muropeptides), produced by muramidase digestion of the purified sacculus isolated from Bacillus subtilis (vegetative cell form of the wild type and a dacA mutant) and Bacillus megaterium (endospore form), is outlined based on UV matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and nano-electrospray ionization (nESI) quadrupole ion trap (QIT) mass spectrometry (MS). After enzymatic digestion and reduction of the resulting muropeptides, the complex glycopeptide mixture was separated and fractionated by reversed-phase high-performance liquid chromatography. Prior to mass spectrometric analysis, the muropeptide samples were subjected to a desalting step and an aliquot was taken for amino acid analysis. Initial molecular mass determination of these peptidoglycan fragments (ranging from monomeric to tetrameric muropeptides) was performed by positive and negative ion MALDI-MS using the thin-layer technique with the matrix alpha-cyano-4-hydroxycinnamic acid. The results demonstrated that for the fast molecular mass determination of large sample numbers in the 0.8-10 pmol range and with a mass accuracy of +/-0.07%, negative ion MALDI-MS in the linear TOF mode is the method of choice. After this kind of muropeptide screening often a detailed primary structural analysis is required owing to ambiguous data. Structural data could be obtained from peptidoglycan monomers by post-source decay (PSD) fragment ion analysis, but not from dimers or higher oligomers and not with the necessary sensitivity. Multistage collision-induced dissociation (CID) experiments performed on an nESI-QIT instrument were found to be the superior method for structural characterization of not only monomeric but also of dimeric and trimeric muropeptides. Up to MS4 experiments were sometimes necessary to obtain unambiguous structural information. Three examples are presented: (a) CID MSn (n = 2-4) of a peptidoglycan monomer (disaccharide-tripeptide) isolated from B. subtilis (wild type, vegetative cell form), (b) CID MSn (n = 2-4) of a peptidoglycan dimer (bis-disaccharide-tetrapentapeptide) obtained from a B. subtilis mutant (vegetative cell form) and (c) CID MS2 of a peptidoglycan trimer (a linear hexasaccharide with two peptide side chains) isolated from the spore cortex of B. megaterium. All MS(n) experiments were performed on singly charged precursor ions and the MS2 spectra were dominated by fragments derived from interglycosidic bond cleavages. MS3 and MS4 spectra exhibited mainly peptide moiety fragment ions. In case of the bis-disaccharide-tetrapentapeptide, the peptide branching point could be determined based on MS3 and MS4 spectra. The results demonstrate the utility of nESI-QIT-MS towards the facile determination of the glycan sequence, the peptide linkage and the peptide sequence and branching of purified muropeptides (monomeric up to trimeric forms). The wealth of structural information generated by nESI-QIT-MSn is unsurpassed by any other individual technique.

[MALD-MS in the quantitative analysis of peptides and proteins]

A modified method of isotope dilution was applied to the quantitative determination of peptides and proteins by MALDI MS at subpicomolar level. The essence of the method consists in the quantitative analysis of the enzymic hydrolysis products rather than the starting compounds. This allows the measurements to be performed at a higher resolution and makes the method independent of the molecular mass of oligopeptides and proteins examined. Fragments obtained by hydrolysis of the same oligopeptide or protein in a known concentration by the same enzyme and labeled with the stable 18O isotope are used as internal standards. The label is introduced by carrying out the hydrolysis in H(2)18O, and the oligopeptide concentration is calculated from the isotope distribution between the labeled and unlabeled hydrolysis products in the mass spectrum. This method was tested in the determination of concentrations of the angiotensinogen (1-14) fragment (oligopeptide), extracellular RNAase from Bacillus amyloliquefaciens (protein) and its protein inhibitor, barstar M. Usefulness of this method in kinetic studies was also demonstrated.

Quantification of the amount of galacturonic acid residues in blocksequences in pectin homogalacturonan by enzymatic fingerprinting with exo- and endo-polygalacturonase II from Aspergillus niger

A method to determine the amount of galacturonic acid in blocksequence (BS) in pectin homogalacturonan (HG) is described. The method is based on a combination of endopolygalacturonase II (endo-PG II) and exopolygalacturonase (exo-PG) digestion followed by quantification of the liberated galacturonic acid monomer. The amount of monomers released is directly related to the amount of non-esterified galacturonic acid units located between two other non-esterified galacturonic acids units on the HG chain. The amount released for exo-PG digestion only corresponds to the BS located at the non-reducing end of the polymer. The difference between total- and exo-BS was calculated to be the amount of endo-BS located either within or on the reducing end of the HG. Three series of model pectins obtained by de-esterification of a high-ester pectin with either plant pectin methyl-esterase (p-PME, P-series), fungal pectin methyl-esterase (f-PME, F-series) and chemical de-esterification using base (B-series) were analysed and compared with a fully de-esterified pectic acid sample obtained from the same raw material. Clear differences for the increase of the amounts of blocksequence could be seen between de-esterification of the P- and F-series samples supporting a blockwise and a homogenous de-esterification mechanism, respectively. f-PME and base treatment showed only minor differences in the increase of galacturonic acid units in BS, despite differences seen in their methyl-esterification pattern. Differences between the amounts of galacturonic acid located in exo- and endo-BS, provided evidence for the need of a certain start side or blocklength for p-PME to de-esterify blockwise.

Analysis of different de-esterification mechanisms for pectin by enzymatic fingerprinting using endopectin lyase and endopolygalacturonase II from A. niger

A series of pectins with different distribution patterns of methyl ester groups was produced by treatment with either plant (p-PME) or fungal pectin methyl esterases (f-PME) and compared with those obtained by base catalysed de-esterification. The products generated by digestion of these pectins with either endopectin lyase (PL) or endopolygalacturonase II (PG II) from Aspergillus niger were analysed using matrix assisted laser desorption ionisation mass spectrometry (MALDIMS) and high-performance anion-exchange chromatography with pulsed amperometric or UV detection (HPAEC-PAD/UV). Time course analysis using MALDIMS was used to identify the most preferred substrate for each enzyme. For PL, this was shown to be fully methyl esterified HG whereas for PG II, long regions of HG without any methyl esterification, as produced by p-PME was the optimal substrate. The blockwise de-esterification caused by p-PME treatment gave a decrease of partly methylated oligomers in PL fingerprints, which did not effect the relative composition of partly methylated oligomers. PG II fingerprints showed a constant increase of monomers and oligomers without any methyl ester groups with decreasing degree of esterification (DE), but almost no change in the concentration of partly methylated compounds. PL fingerprints of f-PME and chemically treated pectins showed decreasing amounts of partly methyl esterified oligomers with decreasing DE, together with a relative shift towards longer oligomers. PG II fingerprints were characterised by an increase of partly methylated and not methylated oligomers with decreasing DE. But differences were also seen between these two forms of homogenous de-esterification. Introduction of a certain pattern of methyl ester distribution caused by selective removal of certain methyl ester groups by f-PME is the most reasonable explanation for the detected differences.

Quantitation of peptides and proteins by matrix-assisted laser desorption/ionization mass spectrometry using (18)O-labeled internal standards

A method for quantitating proteins and peptides in the low picomole and sub-picomole range has been developed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with internal (18)O-labeled standards. A simple procedure is proposed to produce such internal standards for the tested sample by enzymatic hydrolysis of the same sample (with known concentration) in (18)O-water. A mathematical algorithm was developed which uses the isotopic patterns of the substance, the internal standard, and the substance/internal standard mixture for accurate quantitation of the substance. A great advantages of the proposed method is the absence of molecular weight limitation for the protein quantitation and the possibility of quantitation without previous fractionation of proteins and peptides. Using this strategy, the peptide angiotensinogen and two proteins, RNase and its protein inhibitor, were quantified by MALDI-time-of-flight (TOF) mass spectrometry.

Quantitation of peptides and proteins by matrix-assisted laser desorption/ionization mass spectrometry using (18)O-labeled internal standards

A method for quantitating proteins and peptides in the low picomole and sub-picomole range has been developed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with internal (18)O-labeled standards. A simple procedure is proposed to produce such internal standards for the tested sample by enzymatic hydrolysis of the same sample (with known concentration) in (18)O-water. A mathematical algorithm was developed which uses the isotopic patterns of the substance, the internal standard, and the substance/internal standard mixture for accurate quantitation of the substance. A great advantages of the proposed method is the absence of molecular weight limitation for the protein quantitation and the possibility of quantitation without previous fractionation of proteins and peptides. Using this strategy, the peptide angiotensinogen and two proteins, RNase and its protein inhibitor, were quantified by MALDI-time-of-flight (TOF) mass spectrometry.

Sequencing of partially methyl-esterified oligogalacturonates by tandem mass spectrometry and its use to determine pectinase specificities

Complex mixtures of acidic oligosaccharides were produced by enzymatic digestion of partially methyl-esterified pectin with Aspergillus niger pectin lyase, endopolygalacturonase II, and exopolygalacturonase. To determine the specificities of these pectolytic enzymes toward non-esterified and methyl-esterified galacturonic acid residues, we have studied the methyl esterification patterns of selected oligomers in unseparated pectin digests. Collision-induced dissociation in a nanoelectrospray ionization ion trap mass spectrometer was used to locate methyl-esterified galacturonic acid residues in oligomers up to a degree of polymerization of 10. Analysis of the methyl esterification patterns gave insight into the substrate specificities of these pectolytic enzymes. Isomeric fragment ions containing the reducing and nonreducing ends were differentiated by 18O-labeling of the reducing end.

Matrix-assisted laser desorption/ionization time-of-flight and nano-electrospray ionization ion trap mass spectrometric characterization of 1-cyano-2-substituted-benz[f]isoindole derivatives of peptides for fluorescence detection

A series of hexa- to decapeptides (molecular mass range 800-1200) were labeled with naphthalene-2,3-dicarboxaldehyde, which preferentially reacts with the primary amino groups of a peptide. A highly stable peptide conjugate is formed, which allows selective analysis by fluorescence at excitation and emission wavelengths of 420 and 490 nm, respectively. After removal of unreacted compounds, the peptide conjugates were characterized by matrix-assisted laser desorption/ionization (MALDI) time-of-flight and nano-electrospray ionization (ESI) ion trap mass spectrometry. They readily form both [M + H]+ ions by MALDI and both [M + H]+ and [M + 2H]2+ ions by ESI. Furthermore, the fragmentation behavior of the N-terminally tagged peptides, exhibiting an uncharged N-terminus, was investigated applying post-source decay fragmentation with a curved field reflector and collision-induced dissociation with a quadrupole ion trap. Fragmentation is dominated in both cases by series of a-, b- and y-type ions and [M + H - HCN]+ ions. Peptide bonds adjacent to the fluorescence label were less susceptible to cleavage than the bonds of the non-derivatized peptide ions. In general, the resulting fragment ion patterns were less complex than those of the underivatized peptides.

Characterization of enzymatic pectin digests by matrix-assisted laser desorption/ionization mass spectrometry

The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the characterization of partially methyl-esterified enzymatic pectin digests is described. The sensitivities of several matrices, positive and negative ion modes and desalting techniques for these acidic oligosaccharides were compared. The most favorable results were obtained with a thin-layer preparation of a mixture of 2,4,6-trihydroxyacetophenone and nitrocellulose in the negative ion mode. Results are presented demonstrating the sensitive characterization of separated and unseparated high-ester pectin digests obtained after complete digestion using Aspergillus niger pectin lyase and the analysis of digests after chemical modification. In the case of unseparated digests, the analysis of methylation patterns is demonstrated. Oligomers with a degree of polymerization up to 40 were detected after enrichment of large oligomers by propan-2-ol precipitation.

Identification of a gliadin T-cell epitope in coeliac disease: general importance of gliadin deamidation for intestinal T-cell recognition

Coeliac disease probably results from a T-cell response to wheat gliadin and is associated to HLA-DQ2. No gliadin epitopes recognized by intestinal T cells have yet been identified, limiting our understanding of the pathogenesis. Gut-lesion-derived DQ2-restricted T cells from coeliac disease patients were used to identify an epitope within a purified gamma-type gliadin. The structure of the epitope was characterized by mass spectrometry and verified by synthesis. The epitope (QPQQSFPEQQ) results from deamidation of a distinct glutamine in the native structure. This deamidation is important for binding to DQ2 and T-cell recognition. Other gut-derived T cells fail to recognize the epitope, although deamidation of unfractionated gliadin enhances the response of all gut-derived DQ2-restricted T cells isolated from several patients. Several DQ2-restricted T-cell epitopes exist, but for all of them deamidation of glutamine residues appears to be critical for creation of active epitopes. Native gliadin has few negatively charged residues but is very rich in glutamine. After deamidation gliadin becomes a rich source of DQ2 epitopes thus providing a link between DQ2, gliadin and coeliac disease. The necessity for modification may have general immunological relevance.

Tissue transglutaminase selectively modifies gliadin peptides that are recognized by gut-derived T cells in celiac disease

The action of tissue Transglutaminase (TGase) on specific protein-bound glutamine residues plays a critical role in numerous biological processes. Here we provide evidence for a new role of this enzyme in the common, HLA-DQ2 (and DQ8) associated enteropathy, celiac disease (CD). The intestinal inflammation in CD is precipitated by exposure to wheat gliadin in the diet and is associated with increased mucosal activity of TGase. This enzyme has also been identified as the main target for CD-associated anti-endomysium autoantibodies, and is known to accept gliadin as one of its few substrates. We have examined the possibility that TGase could be involved in modulating the reactivity of gliadin specific T cells. This could establish a link between previous reports of the role of TGase in CD and the prevailing view of CD as a T-cell mediated disorder. We found a specific effect of TGase on T-cell recognition of gliadin. This effect was limited to gliadin-specific T cells isolated from intestinal CD lesions. We demonstrate that TGase mediates its effect through an ordered and specific deamidation of gliadins. This deamidation creates an epitope that binds efficiently to DQ2 and is recognized by gut-derived T cells. Generation of epitopes by enzymatic modification is a new mechanism that may be relevant for breaking of tolerance and initiation of autoimmune disease.

Electrophoresis-related protein modification: alkylation of carboxy residues revealed by mass spectrometry

In recent years, the combination of gel electrophoresis and mass spectrometry has developed into one of the most powerful approaches for the analysis of proteins. However, a number of gel electrophoresis-induced protein modifications have been described. Cysteine is the most endangered amino acid readily reacting with mercaptoethanol or free acrylamide. In the course of studies on glucan phosphorylases (E.C.2.4.1.1) from white potato (Solanum tuberosum L.) and the T cell receptor, we noticed that proteolytic peptides from these proteins can undergo an unexpected modification, giving rise to a mass increment of 14 Da. By post-source decay (PSD) analysis the modification was identified as methylation of the glutamic acid side chain carboxyl group. The methylation takes place during Coomassie blue staining of proteins if both trichloroacetic acid and methanol are present in the staining solution. Replacement of methanol by ethanol under otherwise unchanged conditions results in ethylation of the peptides. The in vitro alkylation was further studied by using synthetic peptides which contain, at different positions: glutamic acid, aspartic acid or the corresponding amides. The kinetic analysis of the observed reactions revealed that glutamic acid is preferentially methylated. The three other amino acid residues can be methylated but with a velocity at least one order of magnitude lower. Although these modifications complicate the interpretation of the spectra, they provide valuable structural information.

Nano electrospray combined with a quadrupole ion trap for the analysis of peptides and protein digests

A nano electrospray (NanoES)/ion trap combination was developed to take advantage of the long spraying time of the NanoES source (Wilm, M. S., Mann, M. Int. J. Mass Spectrom. Ion Processes 1994, 136, 167-180) for extensive experiments on the ion trap. The low flow rate associated with the NanoES allows for optimization of experimental conditions and data acquisition for more than 30 min with 1 µL of solution. Thus, even time-consuming experiments, such as multiple fragmentation steps or the sequencing of many components in a mixture, can be performed with very small volumes of sample. Stored waveform inverse Fourier transformation (SWIFT) signals were used during the injection period to accumulate ions of low intensity and to improve the dynamic range of the quadrupole ion trap. To sequence peptides, a combination of nozzle-skimmer fragmentation, SWIFT accumulation of a single fragment to high intensity, and a second fragmentation step was employed to obtain complete sequence information. Unseparated peptide mixtures were infused and weak portions of the spectrum were enhanced by using the SWIFT method, followed by fragmentation of various accumulated peptide ions.

[The effect of infrared laser rays on herpes simplex virus and the functions of human immunocompetent cells]

In vitro investigations were performed to study the effect of infrared Nd:YAG laser irradiation on herpes simplex virus and the viral replication in herpes-infected Vero cell microcultures. In addition, the influence of laser irradiation on human immuncompetent cells was investigated by irradiation and incubation of herpes-infected cell cultures overlaid with leucocytes and observation of leucocyte migration under agarose after laser irradiation. There was no evidence of herpes simplex virus inactivation by laser irradiation. Irradiation of Vero cell microcultures infected with virus did not influence the development of the viral cytopathic effect. However, irradiated cultures showed an increase of about 50% in the virus yield. Only a slight indication of laser influence on immunocompetent cells was found. Cell cultures incubated with leucocytes (from both seropositive and seronegative donors) and irradiated showed an inhibitory effect with about half the virus yield seen in unirradiated controls. However, there was no relation between the energy applied and yield reduction. In addition, laser light caused no change in leucocyte migration.

Simple methods for the assessment of migration areas in lymphocyte migration under agarose

Two methods are described for the assessment of lymphocyte migration areas. One, based on the principle of point counting, allows precise area determination by the aid of a small, transparent grid. The other, similar method with appropriately spaced circles might be used for the classification of such migration areas whose shape approach a circle.