Physiologie der Megakaryopoiese und des Thrombozyten

Zusammenfassung Thrombozyten werden aus dem Zytoplasma von Megakaryozyten freigesetzt und haben eine entscheidende Funktion bei der Blutgerinnung. Sie sind auch in entzündliche Prozesse und die Wundheilung involviert. Die Proliferation und Differenzierung von Megakaryozyten wird durch die Bindung des Wachstumsfaktors Thrombopoietin (Tpo) an seinen Rezeptor c-Mpl stimuliert und reguliert. Glykoproteine der Thrombozytenmembran vermitteln bei Gefäßverletzung die Bindung von Thrombozyten an das subendotheliale Gewebe und die Aggregation zu hämostatischen Gerinnseln. Störungen der Megakaryopoiese, Thrombozytopoiese und Thrombozytenfunktion verursachen mit oder ohne Thrombozytopenie eine Gerinnungsstörung. Mit der molekularbiologischen Analyse ist es in jüngster Zeit gelungen, die Regulationskaskaden für die Plättchenfunktion, Thrombopoiese und Megakaryopoiese zunehmend besser zu verstehen und auf Krankheiten zu beziehen. Damit verknüpft sich die Hoffnung, gezielter in pathologische Prozesse eingreifen zu können.     

Antecedents of respiratory pauses in extremely low birth weight infants supported by proportional assist ventilation.

OBJECTIVE: To determine characteristics of breathing patterns prior to respiratory pauses in extremely low birth weight (ELBW) infants breathing spontaneously under proportional assist ventilation (PAV). METHODS: Thirteen infants (mean +/- SD: gestational age 25 +/- 1 weeks; birth weight 753 +/- 149 g; age 4 +/- 3 days) were studied. Recordings were obtained under PAV over two-hour periods on two consecutive days. The last 10 breaths preceding respiratory pauses were analyzed. RESULTS: Tidal volume, inspiratory and expiratory peak flow, and mean inspiratory flow decreased in the last breaths prior to respiratory pauses compared to all other breaths (p < 0.001). Of all apneas 89% were preceded by a decrease in tidal volume of at least 33% (435/487; p < 0.001). The positive predictive value of a decrease in tidal volume to predict an apnea was 26% (435/1640; p < 0.001). CONCLUSIONS: Decreases in tidal volume of at least 33% and in airflow are the predominant changes in the breathing pattern prior to respiratory pauses in ELBW infants, preceding 89% of all respiratory pauses. Their low positive predictive value of 26% however, indicates that further variables of breathing need to be implemented to predict cessation of breathing with higher precision.     

Diaphysäre Femurpseudarthrosen – nur ein technisches Problem?

Between 1981 and 1994 at the Bergmannsheil Ruhr University Hospital in Bochum, Germany, we treated 145 patients with femoral diaphyseal nonunions following initial operative treatment. Of these patients, 138 received this initial operative treatment at an outside institution. The primary reconstructions for the fractures utilized plates in 112 cases, reamed nails in 24 cases and external fixators in 9 cases. The average age of the patients was 35 years and the mean time from the initial operative treatment was 2 years. Twenty-seven patients (19%) presented with a hypertrophic nonunion and 118 (81%) with an atrophic nonunion. There was a significant correlation between primary "classic" plating and development of an atrophic nonunion (chi 2-test: P < 0.01). We observed 34 wound infections (23%) with no significant correlation to the type of primary osteosynthesis. We determined that 73 of the pseudarthroses were due to improper osteosynthesis techniques. Of these cases, 41% involved the use of plates, 83% involved the use of reamed nails, and 78% involved the use of external fixators. Fracture location near the diaphyseal-metaphyseal junctions was common in this problematic group. Ninety-two percent of all plates led to atrophic nonunions. There were 21 open fractures and of these 90% (n = 19) developed an atrophic pseudarthrosis and 29% (n = 6) developed a wound infection. Fifty-seven (39%) of all patients had additional injuries, but we found that did not increase the risk of disturbed bone healing. Our revision operations focused on the elimination of wound infections, refreshment of bone healing, and improvement in fragment stability. Only 28% of all "classic" plates and 11% of all external fixators were changed to an intramedullary implant at the time of the first revision surgery. Hypertrophic nonunions required a mean of 1.3 revision operations to achieve bone healing whereas a mean of 2 revision operations were necessary to fuse atrophic bone ends (P < 0.05). In cases of diaphyseal pseudarthrosis healing time was not affected by the type of osteosynthesis used for primary reconstructions. Since lack of fracture healing can often already be observed directly from postoperative X-rays, we recommend that revision procedures be performed early. The prolonged length of time to care for femoral nonunions underlines the importance of appropriate primary fracture treatment. That takes into consideration both the biomechanical and the biological aspects of bone healing.     

A novel metalloprotease from Vipera lebetina venom induces human endothelial cell apoptosis.

A novel endothelial cell apoptosis inducing metalloprotease (VLAIP) was found in the snake venom of Vipera lebetina. This metalloprotease is a heterodimeric glycoprotein with molecular mass of about 106 kDa. The protease hydrolyzes azocasein, fibrinogen and oxidized insulin B-chain. The enzyme readily hydrolyzes the Aalpha-chain and more slowly Bbeta-chain of fibrinogen. VLAIP does not cleave fibrin. The complete amino acid sequences of the two different monomers of VLAIP are deduced from the nucleotide sequences of cDNAs encoding these proteins. The full-length cDNA sequences of the VLAIP-A and VLAIP-B encode open reading frames of 616 and 614 amino acids that include signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. VLAIP belongs to the metalloprotease/disintegrin family of reprolysins and has high identity with the proteins that induce apoptosis of endothelial cells. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes cell death. We demonstrated that VLAIP inhibits endothelial cell adhesion to extracellular matrix proteins: fibrinogen, fibronectin, vitronectin, collagen I, and collagen IV. The induction of apoptosis by VLAIP was shown by means of a typical DNA fragmentation pattern of apoptotic cells as well as by monitoring phosphatidylserine externalization using annexin V-FITC staining and flow cytometric analysis.     

An acquired G-CSF receptor mutation results in increased proliferation of CMML cells from a patient with severe congenital neutropenia.

Severe congenital neutropenia (CN) is characterized by a maturation arrest of myelopoiesis at the promyelocyte stage. Treatment with pharmacological doses of recombinant human granulocyte colony-stimulating factor (rh-G-CSF) stimulates neutrophil production and decreases the risk of major infectious complications. However, approximately 15% of CN patients develop myeloid malignancies that have been associated with somatic mutations in the G-CSF receptor (G-CSFR) and RAS genes as well as with acquired monosomy 7. We report a CN patient with chronic myelomonocytic leukemia (CMML) who never received rh-G-CSF. Molecular analysis demonstrated a somatic G-CSFR mutation (C2390T), which led to expression of a truncated G-CSFR protein in the CMML. Normal G-CSFR expression was unexpectedly absent in primary and cultured CMML. In addition, CMML cells showed monosomy 7 and an oncogenic NRAS mutation. In vitro culture revealed a G-CSF-dependent proliferation of CMML cells, which subsequently differentiated along the monocytic/macrophage lineage. Our results provide direct evidence for the in vivo expression of a truncated G-CSFR in leukemic cells, which emerged in the absence of rh-G-CSF treatment and transduces proliferative signals.     

Tissue Identification of the TMJ Disk and Disk Attachments and Related Vascularization

In this study, the authors described the collagenous tissue of the disk and disk attachments of the temporomandibular joint (TMJ) in Macaca fascicularis monkeys and the area's vascularization. The authors subjected five monkey heads to perfusion fixation and removed the right TMJ en bloc. After decalcification and sectioning, the sections were routinely stained for tissue identification and examined in polarized light. Frozen sections from the six TMJs from three unfixed monkey heads were used for enzyme histochemistry.

The dense collagenous tissue of the disk contained no chondrocytes. In polarized light the dense central biconcave part demonstrated birefringence throughout the entire thickness of the disk. This indicates parallel orientation of the fibers, which run in an anteroposterior direction. Within the anterior and posterior bands, the fibers spread out towards the attachments.

Enzyme histochemistry showed vessels within the loose connective tissue of the attachments, but no vessels were seen to penetrate into the dense connective tissue forming the disk. The vascularized fascia of the upper part of the superior lateral pterygoid muscle continued into the disk. The muscle fibers did not run into the disk but appeared in the anterior part of the capsule and inserted into the condylar neck.     

Particulate vs. block bone grafts: Three-dimensional changes in graft volume after reconstruction of the atrophic maxilla,a 2-year radiographic follow-up

BackgroundExtensive alveolar bone resorption in the maxilla limits the possibility of successful placement and osseointegration of endosseous implants for future prosthetic rehabilitation. Autogenous bone from the iliac crest may be used as lateral onlays in the atrophic maxilla, both as block and particulate bone. To our knowledge, there is no three-dimensional 2-year follow-up study measuring the volumetric reduction of the augmented areas comparing particulate and block bone grafts.PurposeThe aim of this study was to conduct a radiographic 2-year follow-up study, using computed tomographic (CT) images in order to evaluate and compare the extent of bone graft resorption in the frontal maxillae augmented by particulate (test) and block bone (control).Material and methodsEleven patients treated with iliac bone grafts and oral implants in the maxilla were followed with CT examinations directly post grafting and after 2 years.ResultThe volumetric changes after 6 months were extensive. Additionally, the changes in particulate bone tended to be larger after 2 years compared to block bone, using this protocol. However, the difference was not statistically significant.ConclusionThe present follow-up study showed that there is radiographically complete integration and embedding of implants installed in grafted bone despite extensive initial graft resorption. There was no significant difference in the amount of volumetric reduction between particulate bone and block bone grafts.     

Parents’ experiences of an instrumental vaginal birth findings from a regional survey in Sweden

ObjectiveAn instrumental vaginal birth is known to affect women’s birth experience, few studies have explored the fathers’ experiences of attending such a birth. The aim of this study is to compare birth outcome and parents’ feelings in parents with instrumental vaginal birth or a spontaneous vaginal birth.MethodsA regional survey was conducted of 936 mothers and 827 fathers recruited in mid-pregnancy and followed up 2 months after birth. Data was collected by questionnaires. Crude and adjusted odds ratios with a 95% confidence interval were used in the analysis.ResultsThe prevalence for instrumental vaginal birth was 9%. Prolonged labour (OR 8.3; 95% CI 5.0–13.9), augmentation with synthetic oxytocin (OR 5.1; 2.9–8.9), and birth complications (OR 2.5; 1.5–2.6) were more common in the instrumental vaginal group. An instrumental vaginal birth was associated with a negative birth experience for mothers (OR 3.2; 1.3–8.1) and fathers (OR 5.2; 1.2–21.5). Mothers who had an instrumental vaginal birth were more likely to report feelings that the baby would be damaged during birth (OR 3.0; 1.7–5.5) and that the birth experience made them decide not to have any more children (OR 3.4; 1.1–10.7). Fathers reported a near-panic feeling when attending an instrumental vaginal birth (OR 5.2; 1.7–15.5).ConclusionAn instrumental vaginal birth was correlated with longer and more complicated births, epidurals and oxytocin augmentation. It affected the birth outcome and parents’ feelings and was associated with future reproductive thoughts and a negative birth experience.