Ischemic A/D transition of mitochondrial complex I and its role in ROS generation

Mitochondrial complex I (NADH:ubiquinone oxidoreductase) is a key enzyme in cellular energy metabolism and provides approximately 40% of the proton-motive force that is utilized during mitochondrial ATP production. The dysregulation of complex I function – either genetically, pharmacologically, or metabolically induced – has severe pathophysiological consequences that often involve an imbalance in the production of reactive oxygen species (ROS). Slow transition of the active (A) enzyme to the deactive, dormant (D) form takes place during ischemia in metabolically active organs such as the heart and brain. The reactivation of complex I occurs upon reoxygenation of ischemic tissue, a process that is usually accompanied by an increase in cellular ROS production. Complex I in the D-form serves as a protective mechanism preventing the oxidative burst upon reperfusion. Conversely, however, the D-form is more vulnerable to oxidative/nitrosative damage. Understanding the so-called active/deactive (A/D) transition may contribute to the development of new therapeutic interventions for conditions like stroke, cardiac infarction, and other ischemia-associated pathologies. In this review, we summarize current knowledge on the mechanism of A/D transition of mitochondrial complex I considering recently available structural data and site-specific labeling experiments. In addition, this review discusses in detail the impact of the A/D transition on ROS production by complex I and the S-nitrosation of a critical cysteine residue of subunit ND3 as a strategy to prevent oxidative damage and tissue damage during ischemia–reperfusion injury.

EFFECTS OF ENVIRONMENTAL ANTIOXIDANTS ON PRO-ANGIOGENIC ROS SIGNALLING IN ENDOTHELIAL COLONY FORMING CELLS IN VITRO

Introduction. Endothelial colony-forming cells (ECFCs) hold great cytotherapeutic potential for ischaemic disease. Whilst increasing evidence supports a key role for reactive oxygen species (ROS), specifically those derived from Nox NADPH oxidases, in the underlying angiogenic processes of these and other endothelial cells, such studies investigating the role of redox signalling may be hampered by the standard inclusion of antioxidant agents in endothelial cell media, such as phenol red. Aims. To study the effects of antioxidants present in culture media on pro-angiogenic function of ECFCs in vitro. Methods. Human ECFCs isolated from umbilical cord blood were maintained in media with and without antioxidant components (EGM2 and phenol red-free DMEM, respectively) prior to treatment with pro-oxidant PMA and assessment of their in vitro migratory capacity using a scratch-wound assay to measure pro-angiogenic activity. Results. Our previous work in our group indicated that PMA (500nM) increased ECFC migration in a both a superoxide and NADPH oxidase-dependent manner (control 18.6±2.8, PMA 32.7±6.6% wound closure; n=6, P<0.05), as indicated by attenuation with PEG-SOD and VAS2870. However, inconsistencies in the data generated under varying experimental conditions led us to hypothesise that antioxidant agents in the standard ECFC media may be influencing these effects. Indeed, a direct comparison of cell migration between ECFCs incubated in EGM2 DMEM demonstrated a clear trend towards higher migration in the latter (EGM2 9.0±4.5, DMEM 22.7±6.4%; n=3, P=NS). Similar to our previous EGM2 studies, cell migration was potentiated by PMA (control 11.6±1.6, PMA 25.1±2.8%; n=3, P<0.05), but at a lower dose (100nM), which is consistent with a reduction in media antioxidants. Notably, this response was attenuated by VAS2870 (PMA 37.6±7.3, PMA+VAS2870 10.3±2.9%; n=6, P<0.05), underlining a likely role for Nox NADPH oxidases. Conclusion. Taken together, these data indicate that ECFC migration is sensitive to different endothelial cell growth media, which appears to be dependent upon their antioxidant content. Although further experiments, such as quantification of cellular superoxide generation by dihydroethidium fluorescence may be required to confirm a specific role for antioxidants, such blunting of ROS signalling in vitro is clearly an important consideration which may significantly impact upon data interpretation.

An R -matrix with pseudo-states calculation of electron-impact excitation in C 2 +

We have performed an R-matrix with pseudo-states (RMPS) calculation of electron-impact excitation in C2+.Collision strengths and effective collision strengths were determined for excitation between the lowest 24 terms, including all those arising from the 2s3l and 2s4l configurations. In the RMPS calculation, 238 terms (90 spectroscopic and 148 pseudo-state) were employed in the close-coupling (CC) expansion of the target. In order to investigate the significance of coupling to the target continuum and highly excited bound states, we compare the RMPS results with those from an R-matrix calculation that incorporated all 238 terms in the configuration- interaction expansion, but only the lowest 44 spectroscopic terms in the CC expansion. We also compare our effective collision strengths with those from an earlier 12-state R-matrix calculation (Berrington et al 1989 J. Phys. B: At.Mol. Opt. Phys. 22 665). The RMPS calculation was extremely large, involving (N +1)-electron Hamiltonian matrices of dimension up to 36 085, and required the use of our recently completed suite of parallel R-matrix programs. The full set of effective collision strengths fromourRMPS calculation is available at theOakRidgeNationalLaboratoryControlledFusion Atomic Data Center web site. 1.

Passive Intermodulation of Analog and Digital Signals on Transmission Lines with Distributed Nonlinearities: Modelling and Characterization

Passive intermodulation (PIM) often limits the performance of communication systems with analog and digitally-modulated signals and especially of systems supporting multiple carriers. Since the origins of the apparently multiple physical sources of nonlinearity causing PIM are not fully understood, the behavioral models are frequently used to describe the process of PIM generation. In this paper a polynomial model of memoryless nonlinearity is deduced from PIM measurements of a microstrip line with distributed nonlinearity with two-tone CW signals. The analytical model of nonlinearity is incorporated in Keysight Technology’s ADS simulator to evaluate the metrics of signal fidelity in the receive band for analog and digitally-modulated signals. PIM-induced distortion and cross-band interference with modulated signals are compared to those with two-tone CW signals. It is shown that conventional metrics can be applied to quantify the effect of distributed nonlinearities on signal fidelity. It is found that the two-tone CW test provides a worst-case estimate of cross-band interference for two-carrier modulated signals whereas with a three-carrier signal PIM interference in the receive band is noticeably overestimated. The simulated constellation diagrams for QPSK signals demonstrate that PIM interference exhibits the distinctive signatures of correlated distortion and this indicates that there are opportunities for mitigating PIM interference and that PIM interference cannot be treated as noise. One of the interesting results is that PIM distortion on a transmission line results in asymmetrical regrowth of output PIM interference for modulated signals.

Polynomial Model for High-Order and Multi-Carrier Passive Intermodulation Products

Passive intermodulation (PIM) often limits the performance of communication systems, particularly in the presence of multiple carriers. Since the origins of the apparently multiple physical sources of nonlinearity causing PIM in distributed circuits are not fully understood, the behavioural models are frequently employed to describe the process of PIM generation. In this paper, a memoryless nonlinear polynomial model, capable of predicting high-order multi-carrier intermodulation products, is deduced from the third-order two-tone PIM measurements on a microstrip transmission line with distributed nonlinearity. The analytical model of passive distributed nonlinearity is implemented in Keysight Technology’s ADS simulator to evaluate the adjacent band power ratio for three-tone signals. The obtained results suggest that the costly multi-carrier test setups can possibly be replaced by a simulation tool based on the properly retrieved nonlinear polynomial model.

Ferroelectric Vortices and Related Configurations

This chapter discusses that the theoretical studies, using both atomistic and phenomenological approaches, have made clear predictions about the existence and behaviour of ferroelectric (FE) vortices. Effective Hamiltonians can be implemented within both Monte Carlo (MC) and molecular dynamics (MD) simulations. In contrast to the effective Hamiltonian method, which is atomistic in nature, the phase field method employs a continuum approach, in which the polarization field is the order parameter. Properties of FE nanostructures are largely governed by the existence of a depolarization field, which is much stronger than the demagnetization field in magnetic nanosystems. The topological patterns seen in rare earth manganites are often referred to as vortices and yet this claim never seems to be explicitly justified. By inspection, the form of a vortex structure is such that there is a continuous rotation in the orientation of dipole vectors around the singularity at the centre of the vortex.