Hyperoxemia in invasively ventilated COVID-19 patients-Insights from the PRoVENT-COVID study

OBJECTIVE

We determined the prevalences of hyperoxemia and excessive oxygen use, and the epidemiology, ventilation characteristics and outcomes associated with hyperoxemia in invasively ventilated patients with coronavirus disease 2019 (COVID-19).

METHODS

Post hoc analysis of a national, multicentre, observational study in 22 ICUs. Patients were classified in the first two days of invasive ventilation as 'hyperoxemic' or 'normoxemic'. The co-primary endpoints were prevalence of hyperoxemia (PaO2 > 90 mmHg) and prevalence of excessive oxygen use (FiO2 ≥ 60% while PaO2 > 90 mmHg or SpO2 > 92%). Secondary endpoints included ventilator settings and ventilation parameters, duration of ventilation, length of stay (LOS) in ICU and hospital, and mortality in ICU, hospital, and at day 28 and 90. We used propensity matching to control for observed confounding factors that may influence endpoints.

RESULTS

Of 851 COVID-19 patients, 225 (26.4%) were classified as hyperoxemic. Excessive oxygen use occurred in 385 (45.2%) patients. Acute respiratory distress syndrome (ARDS) severity was lowest in hyperoxemic patients. Hyperoxemic patients were ventilated with higher positive end-expiratory pressure (PEEP), while rescue therapies for hypoxemia were applied more often in normoxemic patients. Neither in the unmatched nor in the matched analysis were there differences between hyperoxemic and normoxemic patients with regard to any of the clinical outcomes.

CONCLUSION

In this cohort of invasively ventilated COVID-19 patients, hyperoxemia occurred often and so did excessive oxygen use. The main differences between hyperoxemic and normoxemic patients were ARDS severity and use of PEEP. Clinical outcomes were not different between hyperoxemic and normoxemic patients.

Association between early cumulative fluid balance and successful liberation from invasive ventilation in COVID-19 ARDS patients — insights from the PRoVENT-COVID study: a national, multicenter, observational cohort analysis

Background

Increasing evidence indicates the potential benefits of restricted fluid management in critically ill patients. Evidence lacks on the optimal fluid management strategy for invasively ventilated COVID-19 patients. We hypothesized that the cumulative fluid balance would affect the successful liberation of invasive ventilation in COVID-19 patients with acute respiratory distress syndrome (ARDS).

Methods

We analyzed data from the multicenter observational ‘PRactice of VENTilation in COVID-19 patients’ study. Patients with confirmed COVID-19 and ARDS who required invasive ventilation during the first 3 months of the international outbreak (March 1, 2020, to June 2020) across 22 hospitals in the Netherlands were included. The primary outcome was successful liberation of invasive ventilation, modeled as a function of day 3 cumulative fluid balance using Cox proportional hazards models, using the crude and the adjusted association. Sensitivity analyses without missing data and modeling ARDS severity were performed.

Results

Among 650 patients, three groups were identified. Patients in the higher, intermediate, and lower groups had a median cumulative fluid balance of 1.98 L (1.27–7.72 L), 0.78 L (0.26–1.27 L), and − 0.35 L (− 6.52–0.26 L), respectively. Higher day 3 cumulative fluid balance was significantly associated with a lower probability of successful ventilation liberation (adjusted hazard ratio 0.86, 95% CI 0.77–0.95, P = 0.0047). Sensitivity analyses showed similar results.

Conclusions

In a cohort of invasively ventilated patients with COVID-19 and ARDS, a higher cumulative fluid balance was associated with a longer ventilation duration, indicating that restricted fluid management in these patients may be beneficial.

Trial registration Clinicaltrials.gov (NCT04346342); Date of registration: April 15, 2020.

Graphical abstract

ICONIC study—conservative versus conventional oxygenation targets in intensive care patients: study protocol for a randomized clinical trial

Background

Oxygen therapy is a widely used intervention in acutely ill patients in the intensive care unit (ICU). It is established that not only hypoxia, but also prolonged hyperoxia is associated with poor patient-centered outcomes. Nevertheless, a fundamental knowledge gap remains regarding optimal oxygenation for critically ill patients. In this randomized clinical trial, we aim to compare ventilation that uses conservative oxygenation targets with ventilation that uses conventional oxygen targets with respect to mortality in ICU patients.

Methods

The “ConservatIve versus CONventional oxygenation targets in Intensive Care patients” trial (ICONIC) is an investigator-initiated, international, multicenter, randomized clinical two-arm trial in ventilated adult ICU patients. The ICONIC trial will run in multiple ICUs in The Netherlands and Italy to enroll 1512 ventilated patients. ICU patients with an expected mechanical ventilation time of more than 24 h are randomized to a ventilation strategy that uses conservative (PaO₂ 55–80 mmHg (7.3–10.7 kPa)) or conventional (PaO₂ 110–150 mmHg (14.7–20 kPa)) oxygenation targets. The primary endpoint is 28-day mortality. Secondary endpoints are ventilator-free days at day 28, ICU mortality, in-hospital mortality, 90-day mortality, ICU- and hospital length of stay, ischemic events, quality of life, and patient opinion of research and consent in the emergency setting.

Discussion

The ICONIC trial is expected to provide evidence on the effects of conservative versus conventional oxygenation targets in the ICU population. This study may guide targeted oxygen therapy in the future.

Trial registration

Trialregister.nl NTR7376. Registered on 20 July, 2018.

Practice of tracheostomy in patients with acute respiratory failure related to COVID-19 - Insights from the PRoVENT-COVID study

Objective

Invasively ventilated patients with acute respiratory failure related to coronavirus disease 2019 (COVID–19) potentially benefit from tracheostomy. The aim of this study was to determine the practice of tracheostomy during the first wave of the pandemic in 2020 in the Netherlands, to ascertain whether timing of tracheostomy had an association with outcome, and to identify factors that had an association with timing.

Methods

Secondary analysis of the ‘PRactice of VENTilation in COVID–19’ (PRoVENT–COVID) study, a multicenter observational study, conducted from March 1, 2020 through June 1, 2020 in 22 Dutch intensive care units (ICU) in the Netherlands. The primary endpoint was the proportion of patients receiving tracheostomy; secondary endpoints were timing of tracheostomy, duration of ventilation, length of stay in ICU and hospital, mortality, and factors associated with timing.

Results

Of 1023 patients, 189 patients (18.5%) received a tracheostomy at median 21 [17 to 28] days from start of ventilation. Timing was similar before and after online publication of an amendment to the Dutch national guidelines on tracheostomy focusing on COVID–19 patients (21 [17–28] vs. 21 [17–26] days). Tracheostomy performed ≤ 21 days was independently associated with shorter duration of ventilation (median 26 [21 to 32] vs. 40 [34 to 47] days) and higher mortality in ICU (22.1% vs. 10.2%), hospital (26.1% vs. 11.9%) and at day 90 (27.6% vs. 14.6%). There were no patient demographics or ventilation characteristics that had an association with timing of tracheostomy.

Conclusions

Tracheostomy was performed late in COVID–19 patients during the first wave of the pandemic in the Netherlands and timing of tracheostomy possibly had an association with outcome. However, prospective studies are needed to further explore these associations. It remains unknown which factors influenced timing of tracheostomy in COVID–19 patients.

Effectiveness, safety and efficacy of INTELLiVENT-adaptive support ventilation, a closed-loop ventilation mode for use in ICU patients - a systematic review

Introduction: INTELLiVENT-Adaptive Support Ventilation (INTELLiVENT-ASV), an advanced closed-loop ventilation mode for use in intensive care unit (ICU) patients, is equipped with algorithms that automatically adjust settings on the basis of physiologic signals and patient's activity. Here we describe its effectiveness, safety, and efficacy in various types of ICU patients.Areas covered: A systematic search conducted in MEDLINE, EMBASE, the Cochrane Central register of Controlled Trials (CENTRAL), and in Google Scholar identified 10 randomized clinical trials.Expert opinion: Studies suggest INTELLiVENT-ASV to be an effective automated mode with regard to the titrations of tidal volume, airway pressure, and oxygen. INTELLiVENT-ASV is as safe as conventional modes. However, thus far studies have not shown INTELLiVENT-ASV to be superior to conventional modes with regard to duration of ventilation and other patient-centered outcomes. Future studies are needed to test its efficacy.

Definition and incidence of hypotension in intensive care unit patients, an international survey of the European Society of Intensive Care Medicine

INTRODUCTION

Although hypotension in ICU patients is associated with adverse outcome, currently used definitions are unknown and no universally accepted definition exists.

METHODS

We conducted an international, peer-reviewed survey among ICU physicians and nurses to provide insight in currently used definitions, estimations of incidence, and duration of hypotension.

RESULTS

Out of 1394 respondents (1055 physicians (76%) and 339 nurses (24%)), 1207 (82%) completed the questionnaire. In all patient categories, hypotension definitions were predominantly based on an absolute MAP of 65 mmHg, except for the neuro(trauma) category (75 mmHg, p < 0.001), without differences between answers from physicians and nurses. Hypotension incidence was estimated at 55%, and time per day spent in hypotension at 15%, both with nurses reporting higher percentages than physicians (estimated mean difference 5%, p = 0.01; and 4%, p < 0.001).

CONCLUSIONS

An absolute MAP threshold of 65 mmHg is most frequently used to define hypotension in ICU patients. In neuro(trauma) patients a higher threshold was reported. The majority of ICU patients are estimated to endure hypotension during their ICU admission for a considerable amount of time, with nurses reporting a higher estimated incidence and time spent in hypotension than physicians.

Correction to: Retrospective Assessment of Behavioral Inhibition in Infants and Toddlers: Development of a Parent Report Questionnaire

The original version of this article were unfortunately published with an error in "Methods" section. This has been corrected by publishing this correction article.

Dynamic Protein Adsorption onto Dendritic Polyglycerol Sulfate Self-Assembled Monolayers

Biomaterial surfaces that are in contact with blood are often prone to unspecific protein adsorption and the activation of the blood clotting cascade. Hence, such materials usually must be functionalized with low-fouling or anticoagulant polymer coatings to increase their performance and durability with respect to various applications, for example as implants or in biomedical devices. Many coatings are based on anionic polymers, such as heparin, and are known to have pronounced anticoagulant effects. To assess the ability of a surface to prevent biofouling and to get further insight into its underlying mechanism, studies of the protein adsorption on self-assembled monolayers (SAMs) are often used as a predictive tool. In this article, we synthesized thioctic acid-functionalized dendritic polyglycerol sulfate (dPGS), which is a well-known synthetic heparin mimetic, and immobilized it onto gold model surfaces. The anionic dPGS SAMs were characterized via contact angle measurements and ellipsometry and compared to their neutral dendritic polyglycerol (dPG) counterparts with respect to their single protein adsorption of the two most abundant blood proteins albumin (Alb) and fibrinogen (Fib). In addition, we used QCM-D and ToF-SIMS as complementary techniques to investigate the dynamic, mixed, and sequential adsorption of Alb and Fib. Our results clearly demonstrate an incomplete Vroman effect and indicate the rearrangement of the adsorbed protein layers, which is presumably drive by ionic interactions between the two proteins and the anionic dPGS surface.

Biodegradable Core⁻Multishell Nanocarriers: Influence of Inner Shell Structure on the Encapsulation Behavior of Dexamethasone and Tacrolimus

We here present the synthesis and characterization of a set of biodegradable core⁻multishell (CMS) nanocarriers. The CMS nanocarrier structure consists of hyperbranched polyglycerol (hPG) as core material, a hydrophobic (12, 15, 18, 19, and 36 C-atoms) inner and a polyethylene glycol monomethyl ether (mPEG) outer shell that were conjugated by ester bonds only to reduce the toxicity of metabolites. The loading capacities (LC) of the drugs, dexamethasone and tacrolimus, and the aggregate formation, phase transitions, and degradation kinetics were determined. The intermediate inner shell length (C15) system had the best overall performance with good LCs for both drugs as well as a promising degradation and release kinetics, which are of interest for dermal delivery.

Implementation of a transfusion bundle reduces inappropriate red blood cell transfusions in intensive care - a before and after study

BACKGROUND

Restrictive red blood cell (RBC) transfusion has been widely described in transfusion guidelines. However, compliance with these guidelines is often poor. Therefore, we developed a care bundle for the transfusion of RBCs in intensive care. We investigated the effect of the application of the transfusion bundle on transfusion practice, hypothesising that the implementation of the transfusion bundle would lead to a reduction of inappropriate RBC transfusions.

STUDY DESIGN AND METHODS

We conducted a before and after study between January and December 2014 in a medical-surgical intensive care unit (ICU) of a university hospital in Amsterdam, the Netherlands. The primary outcome was the percentage of appropriate transfusions, referring to those transfusions that were in accordance to the patients' individual preset haemoglobin threshold.

RESULTS

The mean pre-transfusion haemoglobin level was 7·3 g dL^-1 [standard deviation (SD) = 1·15] during baseline and significantly decreased to 7·1 g dL^-1 (SD = 1·04) after transfusion bundle implementation; 95% confidence interval (CI): 0·009-0·308, P-value = 0·04. The number of inappropriate transfusions significantly decreased from 25% (111/439) during baseline to 15% (42/280) during implementation, a difference of 10%; 95% CI: -0·164 to -0·0416, P-value 0·001. This further decreased to 12% (45/370) in the post-implementation phase. A logistic regression analysis showed that the chance to find an appropriate transfusion is approximately twice as high after transfusion bundle implementation.

CONCLUSIONS

Introduction of a transfusion bundle results in a significant reduction of the number of inappropriate RBC transfusions in the medical-surgical ICU. Our results show that the introduction of a transfusion care bundle helps to improve compliance with transfusion guidelines in daily practice.

Synthesis of pH-Cleavable dPG-Amines for Gene Delivery Application

The development of effective nonviral vectors for gene therapy is still a challenge in research, due to the high toxicity of many existing polycationic nanocarriers. In this paper, the development of two pH-cleavable polyglycerol-amine-based nanocarriers is described. The benz-acetal bond represents the pH-sensitive cleavage site between dendritic polyglycerol (dPG) and glycerol-based 1,2-diamines that can complex genetic material. Due to the acid lability of the acetal moiety, the cleavable dPG-amines are less toxic in vitro. Cell-mediated degradation results in non-toxic dPG with low amine functionalization and low molecular weight cleavage products (cp). The genetic material is released because of the loss of multivalent amine groups. Interestingly, the release kinetics at the endosomal pH could be controlled by simple chemical modification of the acetals. In vitro experiments demonstrate the ability of the cleavable dPG-amine to transfect HeLa cells with GFP-DNA, which resulted in cell-compatible cleavage products.

Tailored dendritic core-multishell nanocarriers for efficient dermal drug delivery: A systematic top-down approach from synthesis to preclinical testing

Drug loaded dendritic core-multishell (CMS) nanocarriers are of especial interest for the treatment of skin diseases, owing to their striking dermal delivery efficiencies following topical applications. CMS nanocarriers are composed of a polyglycerol core, connected by amide-bonds to an inner alkyl shell and an outer methoxy poly(ethylene glycol) shell. Since topically applied nanocarriers are subjected to biodegradation, the application of conventional amide-based CMS nanocarriers (10-A-18-350) has been limited by the potential production of toxic polyglycerol amines. To circumvent this issue, three tailored ester-based CMS nanocarriers (10-E-12-350, 10-E-15-350, 10-E-18-350) of varying inner alkyl chain length were synthesized and comprehensively characterized in terms of particle size, drug loading, biodegradation and dermal drug delivery efficiency. Dexamethasone (DXM), a potent drug widely used for the treatment of inflammatory skin diseases, was chosen as a therapeutically relevant test compound for the present study. Ester- and amide-based CMS nanocarriers delivered DXM more efficiently into human skin than a commercially available DXM cream. Subsequent in vitro and in vivo toxicity studies identified CMS (10-E-15-350) as the most biocompatible carrier system. The anti-inflammatory potency of DXM-loaded CMS (10-E-15-350) nanocarriers was assessed in TNFα supplemented skin models, where a significant reduction of the pro-inflammatory cytokine IL-8 was seen, with markedly greater efficacy than commercial DXM cream. In summary, we report the rational design and characterization of tailored, biodegradable, ester-based CMS nanocarriers, and their subsequent stepwise screening for biocompatibility, dermal delivery efficiency and therapeutic efficacy in a top-down approach yielding the best carrier system for topical applications.

Dendritic polyglycerol-poly(ethylene glycol)-based polymer networks for biosensing application

This work describes the formation of a new dendritic polyglycerol-poly(ethylene glycol)-based 3D polymer network as a matrix for immobilization of the redox enzyme periplasmatic aldehyde oxidoreductase to create an electrochemical biosensor. The novel network is built directly on the gold surface, where it simultaneously stabilizes the enzyme for up to 4 days. The prepared biosensors can be used for amperometric detection of benzaldehyde in the range of 0.8-400 μM.

A microgel construction kit for bioorthogonal encapsulation and pH-controlled release of living cells

pH-Cleavable cell-laden microgels with excellent long-term viabilities were fabricated by combining bioorthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) and droplet-based microfluidics. Poly(ethylene glycol)dicyclooctyne and dendritic poly(glycerol azide) served as bioinert hydrogel precursors. Azide conjugation was performed using different substituted acid-labile benzacetal linkers that allowed precise control of the microgel degradation kinetics in the interesting pH range between 4.5 and 7.4. By this means, a pH-controlled release of the encapsulated cells was achieved upon demand with no effect on cell viability and spreading. As a result, the microgel particles can be used for temporary cell encapsulation, allowing the cells to be studied and manipulated during the encapsulation and then be isolated and harvested by decomposition of the microgel scaffolds.

Manual hyperinflation is associated with a low rate of adverse events when performed by experienced and trained nurses in stable critically ill patients--a prospective observational study

BACKGROUND

Manual hyperinflation (MH) can be performed as part of airway management in intubated and mechanically ventilated patients to mobilize airway secretions. Although previous studies demonstrated MH to be associated with hemodynamic and respiratory instability, we hypothesized MH to cause fewer adverse events (AEs) when performed by experienced and trained nurses in stable critically ill patients.

METHODS

The incidence and type of AEs associated with MH were studied in a 28-bed mixed medical-surgical Intensive Care Unit. A difference in mean arterial pressure (MAP) or heart rate (HR) >15%, a decrease in peripheral oxygen saturation (SpO2) >5%, and a change in end-tidal (et)-CO2 >20% were considered AEs. A decrease of MAP to ≤60 mmHg, any new arrhythmia, and a decrease of SpO2 ≤90% were all considered severe AEs. Also, all changes in medication were considered severe AEs.

RESULTS

A total of 107 MH maneuvers in 74 patients, performed by 57 nurses, were observed and analyzed. A total of 17 MH maneuvers (16%) were associated with any AE; 7 maneuvers (6%) were associated with a severe AE. Overall, MH did not affect MAP. MH caused a statistically significant but clinically irrelevant increase of HR (from 87±24 to 89±22 bpm). In one patient the MAP dropped from 70 mmHg to 60 mmHg, requiring adjustment of vasopressor therapy; one patient developed ventricular tachycardia requiring electric cardioversion. In general, MH did not affect SpO2. In one patient SpO2 dropped below 90%, requiring additional oxygen supply for 10 minutes. MH caused a statistically significant but clinically irrelevant increase of et-CO2 levels (from 4.4±0.9 to 4.5±1.0 kPa). Five patients developed anxiety/agitation during or shortly after MH, mandating additional sedation in four patients. Occurrence of (severe) AEs was not associated with any specific patient or MH characteristic.

CONCLUSION

The rate of hemodynamic and respiratory AEs with MH is low when performed by experienced and trained nurses in stable, critically ill patients. MH, however, may induce or increase anxiety/agitation. We consider MH a safe maneuver in stable ICU patients in our setting.

Highly informative nature of inter simple sequence repeat (ISSR) sequences amplified using tri- and tetra-nucleotide primers from DNA of cauliflower (Brassica oleracea var. botrytis L.)

Inter simple sequence repeat (ISSR) sequences as molecular markers can lead to the detection of polymorphism and also be a new approach to the study of SSR distribution and frequency. In this study, ISSR amplification with nonanchored primer was performed in closely related cauliflower lines. Fourty-four different amplified fragments were sequenced. Sequences of PCR products are delimited by the expected motifs and number of repeats, which validates the ISSR nonanchored primer amplification technique. DNA and amino acids homology search between internal sequences and databases (i) show that the majority of the internal regions of ISSR had homologies with known sequences, mainly with genes coding for proteins implicated in DNA interaction or gene expression, which reflected the significance of amplified ISSR sequences and (ii) display long and numerous homologies with the Arabidopsis thaliana genome. ISSR amplifications revealed a high conservation of these sequences between Arabidopsis thaliana and Brassica oleracea var. botrytis. Thirty-four of the 44 ISSRs had one or several perfect or imperfect internal microsatellites. Such distribution indicates the presence in genomes of highly concentrated regions of SSR, or "SSR hot spots." Among the four nonanchored primers used in this study, trinucleotide repeats, and especially (CAA)5, were the most powerful primers for ISSR amplifications regarding the number of amplified bands, level of polymorphism, and their nature.

[Introduction to vascular engineering]

Vascular engineering developed through advancing knowledge of the physiological and pathological processes operating in cells and tissues subjected to environmental mechanical stress. We review briefly the more relevant cellular and general mechanism characteristic of vascular tissue examining the performances obtained with prosthetic materials (allografts, synthetic grafts) and current research and development of new vessel substitutes (biohybrids or biovessels).

Analysis of Euglena gracilis alpha-, beta- and gamma-tubulin genes: introns and pre-mRNA maturation

We have cloned and analyzed alpha-, beta- and gamma-tubulin genes from Euglena gracilis. The gamma-tubulin genes are 6-10 times longer than the alpha- and beta-tubulin genes, owing to the presence of numerous introns. These introns are all of the conventional type, whereas the alpha- and beta-tubulin genes contain both conventional and non-conventional introns. This is the first time that both types of introns have been found in the same gene. In the E. gracilis genome there are two genes for each tubulin, but the level of gamma-tubulin mRNA is 60 times lower than that of alpha- and beta-tubulin RNAs. The distinctive structure of gamma-tubulin genes prompted us to investigate the maturation of its pre-mRNA. We show that trans-splicing occurs before the cis-splicing of the first intron of the pre-mRNA and that polyadenylation occurs after the cis-splicing of the last intron of the pre-mRNA. We propose that mRNA processing is likely to play a role in regulating the amounts of different tubulins in E. gracilis.

Characterization of trans-splicing in Euglenoids

We have looked for trans-splicing of nuclear mRNAs in several Euglenoid species. In Cyclidiopsis acus, Phacus curvicauda, Rhabdomonas costata and Menoidium pellucidum we showed that several premRNAs chosen at random are matured by a transsplicing process: we identified SL-RNA genes whose 5' ends (SLs for spliced leader-sequences) were transferred to the 5' extremities of mRNAs. The SL-RNA genes are located on repeated DNA fragments which also encode 5S rRNA in P. curvicauda and C. acus. The potential secondary structures of SL-RNAs are compared to those previously characterized in two other Euglenoids: Euglena gracilis and Entosiphon sulcatum. In another Euglenoid species, Distigma proteus, since none of the mRNAs examined were trans-spliced, it is possible that trans-splicing does not occur. Phylogeny based on 5S rRNA sequences suggests that the species which have, or have had, chloroplasts (E. gracilis, P. curvicauda, C. acus) diverged early from the others.

Trans-splicing and cis-splicing in the colourless Euglenoid, Entosiphon sulcatum

The colourless Euglenoid Entosiphon sulcatum is thought to have diverged before the symbiotic event which gave rise to the photosynthetic Euglenoid species as Euglena gracilis. We have isolated genes encoding spliced leader-sequence RNA (SL-RNA) and we show that pre-mRNAs are matured via a trans-splicing reaction in E. sulcatum, as in the case of E. gracilis. The 2.5-kb repeated DNA fragment which encodes the SL-RNA gene also encodes a 5S rRNA gene as well as the genes for the small nuclear (sn) RNAs U1, U2 and U5. The presence of snRNA U1 indicates that the classical cis-splicing mechanism also exists in E. sulcatum. In addition, we show that the E. sulcatum beta-tubulin gene has the intron borders GU-AG, typical of spliceosome-matured introns which have not yet been found in E. gracilis. The probable origins of trans- and cis-mechanisms in Euglenoids are discussed.

[New automatic test for the study of platelet response to variations in osmotic pressure: application in the evaluation of the viability of platelet concentrates]

Studying the osmotic resistance or swelling of platelets has often been suggested as a global test to assess the viability of those cells. A number of authors have also analysed the behaviour of platelets in hypotonic media by a variety of complementary methods (cell count, morphology, determinations of substances released, photometric measurement of aggregation induced by aggregating agents, etc). Most studies are currently based on the so-called "osmotic shock response" test, which measures according to time the light transmitted through platelet-rich plasma (PRP) after dilution in distilled water. In this study, the authors describe a new automated and reproducible test using slow dialysis to assess platelet osmotic resistance. The "Fragilimeter", a device initially described by the authors to characterise RBC fragility, has been adapted to the study of platelet osmotic behaviour. The variations in light transmission through a platelet suspension according to NaCl concentration are linked to the change in cellular volume and lysis and characterise the viability of the cells. The results obtained with normal platelets revealed the good reproducibility of the technique. The osmotic resistance is evaluated for two parameters: anticoagulant (citrate, EDTA) and cellular concentration. The test was applied to quality control of stored platelet concentrates for transfusion, prepared with different cell separators.

Structure and expression of Euglena gracilis nuclear rbcS genes encoding the small subunits of the ribulose 1,5-bisphosphate carboxylase/oxygenase: a novel splicing process for unusual intervening sequences?

In the protist Euglena gracilis, the small subunit of the chloroplast enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase is encoded by nuclear rbcS genes and synthesized as a polyprotein precursor containing eight mature small subunit molecules. This large precursor is encoded by at least eight different nuclear genes as ascertained by transcript analysis. The structure of three rbcS genes was established and the coding sequences were found to be interrupted by many intervening sequences (IVS). Apart from the first 5' intron involved in trans-splicing, none of these IVSs obeys the GT-AG rule characteristic of introns in higher eukaryote genes. Surprisingly, these IVSs are located at identical positions within the three genes studied. Moreover, extensive sequence homologies were found between IVSs located in the same gene as well as in different genes. The sequences of these homologous IVSs differ only by inserted and/or deleted sequences. The striking conservation of the 5' and 3' regions of these IVSs is correlated to their potential secondary structures. These structures, which bring the IVS extremities together with the exon boundaries, could be involved in a novel splicing process. The second 5' IVS is shown to be excised before the addition of the spliced leader sequence to the pre-mRNA. Similarly, two 3' IVSs are excised before the polyadenylation step. These results suggest that IVS splicing is faster than eukaryotic genomic cis-splicing and involves components other than those of the classical spliceosomes.

Functional and mutated agrocinopine synthase genes on octopine T-DNAs

Agrocinopine synthase genes have so far been detected only on the Agrobacterium tumefaciens nopaline Ti plasmid pTiC58 and on the A. rhizogenes Ri plasmid pRiA4. The TA region of the octopine/cucumopine (o/c) A. vitis Ti plasmid pTiTm4 strongly resembles the TL DNA of biotype I octopine Ti plasmids. In addition, it carries an intact and functional agrocinopine synthase gene close to its left border. TA/TL sequence comparison shows that the biotype I TL region still carries a 5'-deleted acs gene, strongly indicating that this gene was originally part of the TL region and belongs to the "common DNA" region of octopine and nopaline Ti plasmids. Tm4 and C58C1 (pTiTm4) remove agrocinopine A from the medium indicating that pTiTm4 also carries agrocinopine uptake genes. In spite of this, Tm4 and related strains are resistant against agrocin 84. Two o/c Ti plasmids that are closely related to pTiTm4, pTiHm1, and pTiAB3, have a mutated acs gene; whereas Hm1 can still take up agrocinopine A, AB3 cannot. These results yield new insights in the evolution of octopine, nopaline, and o/c strains.

IS870 requires a 5'-CTAG-3' target sequence to generate the stop codon for its large ORF1

The TB regions of the Agrobacterium vitis octopine/cucumopine Ti plasmids constitute a family of related structures. All contain a bacterial insertion element downstream of the TB-iaaM gene, IS870.1. Whereas 43 isolates with octopine/cucumopine Ti plasmids carry only one IS870 copy, strain Ag57 carries a second copy (IS870.2) 3.9 kb to the right of IS870.1 and part of the same TB region. Two other octopine/cucumopine strains carry an IS870 copy on their chromosome (IS870.3). A study of the unmodified insertion sites of IS870.2 and IS870.3, cloned from closely related strains, enabled us to delimit the IS870 elements. IS870 has a size of 1,152 bp and is terminated by inverted repeats. It contains a large open reading frame without a stop codon. However, a stop codon is generated by insertion into the target sequence 5'-CTAG-3'. IS870 is related to five other insertion sequence elements. For two of these, the stop codon of the largest open reading frame is also created by insertion into a CTAG target site.

Role of T-region borders in Agrobacterium host range

The limited host range AB3 strain of Agrobacterium tumefaciens induces tumors by transferring two T-regions, TA and TB. TA is a deleted version of the well-known biotype I octopine TL-region that lacks the iaa and ipt genes, but carries an intact oncogene, gene 6b, and typical left and right border sequences. TB carries two iaa genes that together code for the synthesis of indoleacetic acid. Gene 6b and the iaa gene act synergistically when transferred in a coinoculation experiment. The TA-region of the limited host range isolate Ag57 is related to the TA-region of AB3, but differs from it at several positions. The most significant difference is the absence of the right border region. In spite of this, Ag57 and the exconjugant strain C58C9(pTiAg57) induce normal tumors on Nicotiana rustica and Vitis vinifera. Various experiments indicate that gene 6b of the Ag57 TA-region is active and transferred in spite of the absence of the right border. On N. tabacum, C58C9(pTiAg57) is nononcogenic but becomes oncogenic when the pTiAg57 TA-region is restored by the right TA border sequence of pTiAB3. Thus, the right TA border sequence of the biotype III limited host range strains is required for tumor induction on some hosts, but not on others.

Nucleotide sequence, evolutionary origin and biological role of a rearranged cytokinin gene isolated from a wide host range biotype III Agrobacterium strain

A DNA fragment with homology to the cytokinin (ipt) gene from biotype I Agrobacterium tumefaciens strain Ach5 was cloned from the Ti plasmid of the wide host range biotype III Agrobacterium strain Tm-4 and sequenced. The fragment contains an intact ipt coding sequence. However, the 3' non-coding region of this ipt gene is rearranged due to a 0.9 kb deletion fusing it to the 3' coding region of the neighbouring gene 6a, most of which was found to be deleted. The Tm-4 ipt gene is strongly related to the partially deleted ipt gene of the limited host range biotype III strain Ag162. To test its biological activity, the Tm-4 ipt gene was inserted into a specially constructed, disarmed Ti vector lacking tzs and tested on tobacco, where the rearranged ipt gene induced shoot formation. The cloned Tm-4 ipt gene was mutated with Tn5 and the intact gene on the wild-type Tm-4 Ti plasmid was replaced by the mutated gene. The resulting strain was avirulent on tobacco but normally virulent on the natural host of the wild-type strain Tm-4, grapevine. As the biotype I 6b gene diminishes the effect of a corresponding ipt gene, a larger Tm-4 fragment carrying both the ipt gene and an adjacent 6b-like gene was also tested on tobacco and compared with the Tm-4 ipt fragment alone and with an ipt and 6b/ipt fragment derived from Ach5. The Tm-4 6b gene diminishes the effect of the Tm-4 ipt gene, showing the Tm-4 6b gene to be active as well. The Tm-4 6b/ipt combination is less effective than the Ach5 combination. These results provide further insight into the molecular basis of the host range differences between limited host range and wide host range biotype III Agrobacterium strains and show that the WHR cytokinin gene, although active, does not significantly contribute to tumour formation on the natural host of the WHR biotype III strains, grapevine.

[Hemorrheological changes in 50 monoclonal dysglobulinemias treated by plasma exchange]

Rheological examinations were performed before and after plasma exchanges in 50 patients with monoclonal dysglobulinaemia. The parameters investigated were blood and plasma viscosity, erythrocyte filtrability, erythrocyte aggregation and kinetics of agglutination. The results showed reduction of blood and plasma viscosity and improvement in agglutination kinetics under plasma exchanges. Rheological examinations therefore seem to be useful to follow up blood disorders, notably the hyperviscosity syndrome. They can be performed prophylactically, leading to early plasma exchanges to prevent clinical deterioration.

Experimental approach to rouleau formation. Comparison of three methods

From a clinical point of view, the approach to erythrocyte aggregate or rouleau formation and cohesion is undeniably of great interest. A large number of methods have been suggested for studying this parameter such as: back-scattering of light, nephelometry, ultrasound, etc... In this paper the authors have compared three methods to approach rouleau formation: direct observation of rouleau formation (rheoscope); 'erythrocyte aggregometer': with this technique, the light transmitted by the sample is integrated over a period of time and provides an index (IA); laser reflectometer based on studying the light that is back-scattered by the blood sheared in the gap of a viscometer. The results show that the indexes measured by both reflexion and transmission vary according to hematocrit and reach a maximum value at hematocrit levels of between 30 and 40%. In contrast, observation using the rheoscope did not provide qualitative evidence of this phenomenon.