Ultrasonic characterization of biological tissues

Ultrasonic imaging has become increasingly important as a diagnostic tool in medicine because it is noninvasive and it can provide valuable information otherwise unattainable. However, at present, clinical interpretation of an ultrasonic image still mostly relies on recognition of boundaries and positional relationship of anatomical structures and a subjective analysis of the distribution or texture of echo amplitudes. Other potentially useful information carried back by the echoes is completely discarded. The aim of ultrasonic tissue characterization research is to develop methods to extract additional information from the returned echoes so that tissue pathology or abnormality can be reliably identifed and severity of the pathology objectively assessed with quantitative criteria. A number of ultrasonic parameters including acoustic velocity, impedance, attentuation and scattering, have been utilized in attempting to achieve this goal. In this paper, recent progress in this research will be discussed and relevant results presented.     

Adenosine kinase is inactivated by geminivirus AL2 and L2 proteins

AL2 and L2 are related proteins encoded by geminiviruses of the Begomovirus and Curtovirus genera, respectively. Both are pathogenicity determinants that cause enhanced susceptibility when expressed in transgenic plants. To understand how geminiviruses defeat host mechanisms that limit infectivity, we searched for cellular proteins that interact with AL2 and L2. Here, we present evidence that the viral proteins interact with and inactivate adenosine kinase (ADK), a nucleoside kinase that catalyzes the salvage synthesis of 5'-AMP from adenosine and ATP. We show that the AL2 and L2 proteins inactivate ADK in vitro and after coexpression in Escherichia coli and yeast. We also demonstrate that ADK activity is reduced in transgenic plants expressing the viral proteins and in geminivirus-infected plant tissues. By contrast, ADK activity is increased after inoculation of plants with diverse RNA viruses or a geminivirus lacking a functional L2 gene. Consistent with its ability to interact with multiple cellular kinases, we also demonstrate that AL2 is present in both the nucleus and the cytoplasm of infected plant cells. These data indicate that ADK is targeted by viral pathogens and provide evidence that this "housekeeping" enzyme might be a part of host defense responses. In previous work, we showed that AL2 and L2 also interact with and inactivate SNF1 kinase, a global regulator of metabolism that is activated by 5'-AMP. Together, these observations suggest that metabolic alterations mediated by SNF1 are an important component of innate antiviral defenses and that the inactivation of ADK and SNF1 by the geminivirus proteins represents a dual strategy to counter this defense. AL2 proteins also have been shown to act as suppressors of RNA silencing, an adaptive host defense response. A possible relationship between ADK inactivation and silencing suppression is discussed.     

The "black hole" phenomenon in ultrasonic backscattering measurement under pulsatile flow with porcine whole blood in a rigid tube

The "black hole" phenomenon was further investigated with porcine whole blood under pulsatile flow conditions in a straight rigid tube 120 cm long and of 0.95 cm diameter. A modified Aloka 280 commercial scanner with a 7.5 MHz linear array was used to collect the radio frequency (RF) signal of backscattering echoes from the blood inside the tube. The transducer was located downstream from the entrance and parallel to the longitudinal direction of the tube. The experimental results showed that higher hematocrits enhanced the black hole phenomenon, leading to a more apparent and larger diameter black hole. The black hole was not apparent at hematocrits below 23%. The highest hematocrit used in the experiment was 60%. Beat rates of 20, 40 and 60 beats per minute (bpm) were used, and the black hole became weaker in amplitude and smaller in diameter when the peak flow velocity was increased at each beat rate. These results are consistent with the suggestion in previous work that the black hole arises from insufficient aggregation of red blood cells (RBCs) at the center of the tube because of the low shear rate. At 20 and 40 bpm, the peak flow velocity ranges were 10 approximately 25 cm/s and 18 approximately 27 cm/s, respectively. The black hole was very clear at the minimal peak flow velocity but almost disappeared at the maximal velocities for each beat rate. At 60 bpm, experiments were only performed at one peak flow velocity of 31 cm/s and the black hole was clear. The results showed that the black hole was more pronounced at higher beat rates when the peak velocity was the same. This phenomenon cannot be explained by previous hypotheses. Acceleration seems to be the only flow parameter that varies at different beat rates when peak velocities are the same. Therefore, the influence of acceleration on the structural organization and orientation of RBC rouleaux might be another factor involved in the formation of the black hole in addition to the shear rate. As the entrance length was changed from 110 to 15 diameters (D) in seven steps at the hematocrit of 60%, it was found that a position farther downstream yielded a black hole with a greater contrast relative to the surrounding region, while the backscattering power at the central hypoechoic zone did not increase with increasing entrance length.     

Symmetric and Asymmetric Zeolitic Imidazolate Frameworks (ZIFs)/Polybenzimidazole (PBI) Nanocomposite Membranes for Hydrogen Purification at High Temperatures

High‐performance zeolitic imidazolate frameworks (ZIFs)/polybenzimidazole (PBI) nanocomposites are molecularly designed for hydrogen separation at high temperatures, and demonstrate it in a useful configuration as dual‐layer hollow fibers for the first time. By incorporating as‐synthesized nanoporous ZIF‐8 nanoparticles into the high thermal stability but extremely low permeability polybenzimidazole (PBI), the resultant mixed matrix membranes show an impressive enhancement in H₂ permeability as high as a hundred times without any significant deduction in H₂/CO₂ selectivity. The 30/70 ZIF‐8/PBI dense membrane has a H₂ permeability of 105.4 Barrer and a H₂/CO₂ selectivity of 12.3. This performance is far superior to ZIF‐7/PBI membranes and is the best ever reported data for H₂‐selective polymeric materials in the literature. Meanwhile, defect‐free ZIF‐8‐PBI/Matrimid dual‐layer hollow fibers are successfully fabricated, without post‐annealing and coating, by optimizing ZIF‐8 nanoparticle loadings, spinning conditions, and solvent‐exchange procedures. Two types of hollow fibers targeted at either high H₂/CO₂ selectivity or high H₂ permeance are developed: i) PZM10‐I B fibers with a medium H₂ permeance of 64.5 GPU (2.16 ×10^?8 mol m^?2 s^?1 Pa^?1) at 180°C and a high H₂/CO₂ selectivity of 12.3, and, ii) PZM33‐I B fibers with a high H₂ permeance of 202 GPU (6.77 ×10^?8 mol m^?2 s^?1 Pa^?1) at 180°C and a medium H₂/CO₂ selectivity of 7.7. This work not only molecularly designs novel nanocomposite materials for harsh industrial applications, such as syngas and hydrogen production, but also, for the first time, synergistically combines the strengths of both ZIF‐8 and PBI for energy‐related applications.     

Cofactor-specific modulation of 11beta-hydroxysteroid dehydrogenase 1 inhibitor potency

11beta-hydroxysteroid dehydrogenase 1 regulates the tissue availability of cortisol by interconverting cortisone and cortisol. It is capable of functioning as both a reductase and a dehydrogenase depending upon the surrounding milieu. In this work, we have studied the reaction mechanism of a soluble form of human 11beta-hydroxysteroid dehydrogenase 1 and its mode of inhibition by potent and selective inhibitors belonging to three different structural classes. We found that catalysis follows an ordered addition with NADP(H) binding preceding the binding of the steroid. While all three inhibitors tested bound to the steroid binding pocket, they differed in their interactions with the cofactor NADP(H). Compound A, a pyridyl amide bound more efficiently to the NADPH-bound form of 11beta-hydroxysteroid dehydrogenase 1. Compound B, an adamantyl triazole, was unaffected by NADP(H) binding and the sulfonamide, Compound C, showed preferential binding to the NADP+ -bound form of 11beta-hydroxysteroid dehydrogenase 1. These differences were found to augment significant selectivity towards inhibition of the reductase reaction versus the dehydrogenase reaction. This selectivity may translate to differences in the in vivo effects of 11beta-hydroxysteroid dehydrogenase 1 inhibitors.     

Multiple effects of guanine nucleotides on human platelet adenylate cyclase

We report that the adenylate cyclase system in human platelets is subject to multiple regulation by guanine nucleotides. Previously it has been reported that GTP is either required for or has little effect on the response of the enzyme to prostaglandin E₁. We have found that when platelet lysates were prepared in the presence of 5 mM EDTA, GTP lowered the basal and prostaglandin E₁-stimulated adenylate cyclase activity when the enzyme was assayed in the presence of Mg²⁺. The basal and prostaglandin E₁-stimulated adenylate cyclase activities were also increased by washing, which presumably removes endogenous GTP. The analog, guanyl-5′-yl-imidodiphosphate mimics the inhibitory effect of GTP on prostaglandin E₁-stimulated adenylate cyclase activity but it stimulates basal enzyme activity. The onset of the inhibitory effect of GTP on the adenylate cyclase system is rapid (1 min) and is maintained at a constant rate during incubation for 10 min. GTP and guanyl-5′-yl-imidodiphosphate were noncompetitive inhibitors of prostaglandin E₁. An increase in the concentration of Mg²⁺ gradually reduces the effect of GTP while having little influence on the effect of guanyl-5′-yl-imidodiphosphate. Neither the substrate concentration nor the pH (7.2–8.5) is related to the inhibitory effect of guanine nucleotides. The inhibition by nucleotides was found to show a specificity for purine nucleotides with the order of potency being guanyl-5′-yl-imidodiphosphate > dGTP > GTP > ITP > XTP > CTP > TTP. The inhibitory effect of GTP is reversible while the effect of guanyl-5′-yl-imidodiphosphate is irreversible. The GTP inhibitory effect was abolished by preparing the lysates in the presence of Ca²⁺. However, the inhibitory effect of guanyl-5′-yl-imidodiphosphate persisted. Substitution of Mn²⁺ for Mg²⁺ in the assay medium resulted in a diminution of the inhibitory effect of GTP on basal activity and converted the inhibitory effect of GTP on prostaglandin E₁-stimulated activity to a stimulatory effect. At a lower concentration of Mn²⁺ (less than 2 mM) guanyl-5′-yl-imidodiphosphate inhibited prostaglandin E₁-stimulated adenylate cyclase activity, but at a higher concentration of Mn²⁺, it caused an increase in enzyme activity exceeding that occuring in the presence of prostaglandin E₁. In the presence of Mn²⁺, dGTP mimics the effect of GTP and is 50% as effective as GTP. Our data suggest that the inhibitory effect of GTP on prostaglandin E₁-stimulated adenylate cyclase is mainly due to its direct effect on the enzyme itself, whereas the stimulatory effect of GTP on prostaglandin E₁-stimulated adenylate cyclase is due to enhancement of the coupling between the prostaglandin E₁ receptor and adenylate cyclase. These studies also indicate that the method of preparation of platelet lysates can profoundly alter the nature of guanine nucleotide regulation of adenylate cyclase.     

Heterogeneity of leukotriene receptions in guinea-pig trachea

The selective leukotriene (LT) antagonist FPL 55712 antagonized the contractile activity of synthetic LTD₄ and E₄ on guinea-pig trachea. Schild analysis of the antagonism provided evidence for two distinct receptors for LTD₄: one with significantly higher affinity for FPL 55712 than the other. LTE₄ appears to interact preferentially with the high affinity receptor.