Estimation of ABCB1 concentration in plasma membrane

The interaction between ABCB1 transporter and its substrates takes place in cell membranes but the available data precludes quantitative analysis of the interaction between transporter and substrate molecules. Further, the amount of transporter is usually expressed as a number of ABCB1 molecules per cell. In contrast, the substrate concentration in cell membranes is estimated by determination of substrate-lipid partition coefficient, as examples. In this study, we demonstrate an approach, which enables us to estimate the concentration of ABCB1 molecules within plasma membranes. For this purpose, human leukemia K562 cells with varying expression levels of ABCB1 were used: drug selected K562/Dox and K562/HHT cells with very high transporter expression, and K562/DoxDR2, K562/DoxDR1, and K562/DoxDR05 cells with gradually decreased expression of ABCB1 derived from K562/Dox cells using RNA interference technology. First, we determined the absolute amount of ABCB1 in cell lysates using immunoblotting and recombinant ABCB1 as a standard. We then determined the relative portion of transporter residing in the plasma membrane using immunohistochemistry in nonpermeabilized and permeabilized cells. These results enabled us to estimate the concentration of ABCB1 in the plasma membrane in resistant cells. The ABCB1 concentrations in the plasma membrane of drug selected K562/Dox and K562/HHT cells containing the highest amount of transporter reached millimolar levels. Concentrations of ABCB1 in the plasma membrane of resistant K562/DoxDR2, K562/DoxDR1, and K562/DoxDR05 cells with lower transporter expression were proportionally decreased.     

Cyclophosphamide metabolites perforate the apical plasma membranes of urothelial cells in rats

The apical plasma membrane of differentiated superficial urothelial cells is characterised by the presence of asymmetric unit membrane (AUM). Cyclophosphamide (CP) metabolites cause perforation of these thickened membranes. In this study, apical plasma membranes were examined after CP injection by electron microscopy. The immediate effect of the CP metabolites was observed as small round holes appearing, first in the asymmetric apical plasma membrane of terminally differentiated superficial cells, and later in the symmetric apical plasma membrane of exposed undifferentiated intermediate and basal cells. Exposed cells which remained undamaged, immediately underwent maturation of the symmetric apical plasma membrane. These results indicate that CP metabolites perforate the symmetric and asymmetric membranes of most urothelial cells.     

Evolution of an interloop disulfide bond in high-affinity antibody mimics based on fibronectin type III domain and selected by yeast surface display: molecular convergence with single-domain camelid and shark antibodies

The 10th human fibronectin type III domain ((10)Fn3) is one of several protein scaffolds used to design and select families of proteins that bind with high affinity and specificity to macromolecular targets. To date, the highest affinity (10)Fn3 variants have been selected by mRNA display of libraries generated by randomizing all three complementarity-determining region -like loops of the (10)Fn3 scaffold. The sub-nanomolar affinities of such antibody mimics have been attributed to the extremely large size of the library accessible by mRNA display (10(12) unique sequences). Here we describe the selection and affinity maturation of (10)Fn3-based antibody mimics with dissociation constants as low as 350 pM selected from significantly smaller libraries (10(7)-10(9) different sequences), which were constructed by randomizing only 14 (10)Fn3 residues. The finding that two adjacent loops in human (10)Fn3 provide a large enough variable surface area to select high-affinity antibody mimics is significant because a smaller deviation from wild-type (10)Fn3 sequence is associated with a higher stability of selected antibody mimics. Our results also demonstrate the utility of an affinity-maturation strategy that led to a 340-fold improvement in affinity by maximizing sampling of sequence space close to the original selected antibody mimic. A striking feature of the highest affinity antibody mimics selected against lysozyme is a pair of cysteines on adjacent loops, in positions 28 and 77, which are critical for the affinity of the (10)Fn3 variant for its target and are close enough to form a disulfide bond. The selection of this cysteine pair is structurally analogous to the natural evolution of disulfide bonds found in new antigen receptors of cartilaginous fish and in camelid heavy-chain variable domains. We propose that future library designs incorporating such an interloop disulfide will further facilitate the selection of high-affinity, highly stable antibody mimics from libraries accessible to phage and yeast surface display methods.     

Post-Operative Hypertension after Total Knee Arthroplasty and the Effects on Transfusion Rates

Transfusions are a cause of significant patient morbidity as well as expense. Anesthesia literature has examined controlled intraoperative hypotension as a means for reducing blood loss and transfusions. Our hypothesis is that inversely increased blood pressure post-operatively would then lead to increased blood loss and transfusions.We examined 105 consecutive patients who underwent TKA. We found a significant odds ratio of 1.123 for pre-operative hematocrit. For post-operative blood pressure, we calculated an insignificant odds ratio of 1.007, proving no relationship between post-operative blood pressure and transfusions.This is the first study to examine increased post-operative blood pressure''s contribution to transfusion rates. Although we confirmed that low pre-operative hematocrit contributes to increased transfusions, we did not find a relationship between post-operative blood pressure and transfusions.     

Spathidium seppelti foissneri nov. subspec., Spathidium simplinucleatum nov. stat., and Dileptus americanus Kahl, 1931, one new and two poorly known soil gymnostome ciliates from soils of Slovakia

The morphology and infraciliature of three soil gymnostome ciliates, Spathidium seppelti foissneri nov. subspec., Spathidium simplinucleatum nov. stat., and Dileptus americanus, collected from Slovakia, were investigated using live observation and protargol impregnation. S. seppelti foissneri is distinguished from its congeners by a combination of characters including: distinctly spatulate shape with convex oral bulge; 25 ellipsoidal, scattered macronuclear nodules; an average of 23 ciliary rows, 3 anteriorly differentiated to form a dorsal brush occupying 25% of the body length; and rod-shaped to slightly ellipsoidal extrusomes measuring about 5 x 0.5 microm. S. simplinucleatum is about 110 x 50 microm in vivo, characterized by solid, concave oral bulge, with the impression of doubled oral bulge in right side, macronuclear tortuous strand, usually 30 ciliary rows, 3 anteriorly differentiated to form a dorsal brush, and about 7 microm long rod-shaped extrusomes. S. simplinucleatum is highly variable in body size and length of monokinetidal bristle tail. Dileptus americanus is about 300 x 50 microm in vivo and differs from its congeners by a combination of characters including two macronuclear segments with a single micronucleus in between, two contractile vacuoles in dorsal side of trunk, two size types of rod-shaped extrusomes, a proboscis which occupies about 37% of body length, circular oral opening, and an average of 22 ciliary rows, of which up to 4 are differentiated to form a dorsal brush.     

A comparison of tabun-inhibited rat brain acetylcholinesterase reactivation by three oximes (HI-6, obidoxime, and K048) in vivo detected by biochemical and histochemical techniques

Tabun belongs to the most toxic nerve agents. Its mechanism of action is based on acetylcholinesterase (AChE) inhibition at the peripheral and central nervous systems. Therapeutic countermeasures comprise administration of atropine with cholinesterase reactivators able to reactivate the inhibited enzyme. Reactivation of AChE is determined mostly biochemically without specification of different brain structures. Histochemical determination allows a fine search for different structures but is performed mostly without quantitative evaluation. In rats intoxicated with tabun and treated with a combination of atropine and HI-6, obidoxime, or new oxime K048, AChE activities in different brain structures were determined using biochemical and quantitative histochemical methods. Inhibition of AChE following untreated tabun intoxication was different in the various brain structures, having the highest degree in the frontal cortex and reticular formation and lowest in the basal ganglia and substantia nigra. Treatment resulted in an increase of AChE activity detected by both methods. The highest increase was observed in the frontal cortex. This reactivation was increased in the order HI-6 < K048 < obidoxime; however, this order was not uniform for all brain parts studied. A correlation between AChE activity detected by histochemical and biochemical methods was demonstrated. The results suggest that for the mechanism of action of the nerve agent tabun, reactivation in various parts of the brain is not of the same physiological importance. AChE activity in the pontomedullar area and frontal cortex seems to be the most important for the therapeutic effect of the reactivators. HI-6 was not a good reactivator for the treatment of tabun intoxication.