Enhancing Bioelectrochemical Conversion: Molecular Modifications for Amplified Transmembrane Electron Transfer

In Bioelectronics—the confluence of Biology and Electronics—living biological entities are interfaced with electrical components for applications in bioenergy conversion and catalysis, biosensing, medical diagnostics and drug delivery, neural and tissue interrogation, and more. Improving the contacts at biotic-abiotic charge transfer interfaces is therefore of fundamental importance for improving these various bioelectrochemical systems. Here, specific attention is drawn to chemically modifying electrically insulating lipid bilayer membrane interfaces so that biologically-derived electrons may be more readily collected at an electrode. This research is of fundamental scientific interest from a biophysical perspective as well as immense practical importance for bioelectrochemical conversion technologies that interconvert organic fuels and electrical current.Consider microbial bioelectrochemical conversion systems wherein certain bacterial species are commonly employed that have the evolved capacity to directly produce electrical current as a metabolic product. A unifying feature of these species is that they construct conductive membrane-bound redox-protein/cofactor nanostructures for transmembrane electron transport. Drawing inspiration from this molecular functionality, one may envision and synthesize organic semiconducting molecules designed for biological/membrane affinity. The implementation of these materials in living devices for the purpose of amplifying biological transmembrane electron transport is the subject of this dissertation.p-Phenylenevinylene-based conjugated oligoelectrolytes (PPV-COEs) are a class of organic semiconducting molecules designed for membrane modification. Early experiments indicated that PPV-COEs will spontaneously intercalate into lipid bilayer membranes and improve biocurrent outputs, suggesting that PPV-COEs act as transmembrane “molecular wires” for electron transmission. In order to test this hypothesized mechanism, the model lactate-consuming electrogenic bacterium Shewanella oneidensis MR-1 was cultivated and modified with PPV-COEs in microbial three-electrode electrochemical reactors (M3Cs). Because S. oneidensis MR-1 utilizes direct electron transfer (DET) and mediated electron transfer (MET) at distinct potentials, perturbations to the DET and MET current signals in M3Cs provide a view into the mechanism of PPV-COE biocurrent amplification. Results indicate that PPV-COEs statistically improve the coulombic efficiency of S. oneidensis MR-1 lactate-to-current conversion from 51 ± 10% to an exceptional 84 ± 7% (P = 0.0098) by amplifying the native bacterial DET pathway and increasing colonization of the electrode, but PPV-COEs do not appear to act as “molecular wires.”PPV-COEs were next applied to an anaerobic, obligately-crossfeeding (syntrophic) cultures of Pelobacter acetylenicus and Acetobacterium woodii and then to photobioelectrochemical devices based on photosynthetic green plant thylakoid membranes, and these were biochemically and electrochemically characterized. In the former experiments, it was found that PPV-COEs improve reaction rates and intercellular exchange of electron equivalents as a function of molecular length, while in the latter, interfacial contacts and photocurrent were improved as a function of molecular structure and charge distribution; however, direct “molecular wiring” of the organisms to each other and thylakoids to electrodes were again ruled out. Two primary considerations rationalize this result: (a) mismatch of the PPV-COE frontier orbital energies with biological frontier orbital energies and the electrode Fermi energy and (b) the absence of direct electrode contacts.Following this mechanistic insight, a similar experimental approach was extended to two different materials systems. First, a COE with membrane affinity containing a redox-active ferrocene moiety, DSFO+, was synthesized and applied to M3Cs. The frontier orbitals of DSFO+ are energetically aligned with physiological potentials, so DSFO+ catalytically couples to biocurrent production via ferrocene redox activity, remarkably also enabling partial recovery of biocurrent production in non-electrogenic mutant strains of S. oneidensis MR-1. Second, a set of four conjugated polyelectrolytes (CPEs) with systematic variations in backbone structure, pendant ionic functionalities, and the ability to remain doped at neutral pH in aqueous media were synthesized and applied in M3Cs. The self-doped p-type anionic derivative CPE-K is highly conductive and statistically significantly increases steady-state biocurrent output from S. oneidensis MR-1 by 2.7 ± 0.7-fold relative to unmodified controls (P = 0.002). Important structure-property relationships are revealed in these experiments suggesting that anionic pendant groups and the ability to be doped in aqueous media are necessary for CPE biocurrent enhancement. By absorbance spectroscopy, it appears that S. oneidensis MR-1 may de-dope (neutralize) CPE-K, allowing the electrode to re-dope (re-oxidize) it, creating an electronic extension of the electrode. This helps explain the increase in electrode cell colonization from CPE-K. These results provide a foundation for continued improvement of biotic-abiotic contacts with organic semiconductors in Bioelectronic devices

Levels of microparticle tissue factor activity correlate with coagulation activation in endotoxemic mice

Tissue factor (TF) is present in blood in various forms, including small membrane vesicles called microparticles (MPs). Elevated levels of these MPs appear to play a role in the pathogenesis of thrombosis in a variety of diseases, including sepsis

Metal-Insulator Transition in the Two-Dimensional Hubbard Model at Half-Filling with Lifetime Effects within the Moment Approach

We explore the effect of the imaginary part of the self-energy, $Im\Sigma(\vec{k},\omega)$, having a single pole, $\Omega(\vec{k},\omega)$, with spectral weight, $\alpha(\vec{k})$, and quasi-particle lifetime, $\Gamma(\vec{k})$, on the density of states. We solve the set of parameters, $\Omega(\vec{k},\omega$), $\alpha(\vec{k})$, and $\Gamma(\vec{k})$ by means of the moment approach (exact sum rules) of Nolting. Our choice for $\Sigma(k,\omega)$, satisfies the Kramers - Kronig relationship automatically. Due to our choice of the self - energy, the system is not a Fermi liquid for any value of the interaction, a result which is also true in the moment approach of Nolting without lifetime effects. By increasing the value of the local interaction, $U/W$, at half-filling ($\rho = 1/2$), we go from a paramagnetic metal to a paramagnetic insulator, (Mott metal - insulator transition ($MMIT$)) for values of $U/W$ of the order of $U/W \geq 1$ ($W$ is the band width) which is in agreement with numerical results for finite lattices and for infinity dimensions ($D = \infty$). These results settle down the main weakness of the spherical approximation of Nolting: a finite gap for any finite value of the interaction, i.e., an insulator for any finite value of $U/W$. Lifetime effects are absolutely indispensable. Our scheme works better than the one of improving the narrowing band factor, $B(\vec{k})$, beyond the spherical approximation of Nolting.Comment: 5 pages and 5 ps figures (included

Tissue factor: a mediator of inflammatory cell recruitment, tissue injury, and thrombus formation in experimental colitis

There is growing evidence for an interplay between inflammatory and coagulation pathways in acute and chronic inflammatory diseases. However, it remains unclear whether components of the coagulation pathway, such as tissue factor (TF), contribute to intestinal inflammation, and whether targeting TF will blunt the inflammatory cell recruitment, tissue injury, and enhanced thrombus formation that occur in experimental colitis. Mice were fed 3% dextran sodium sulfate (DSS) to induce colonic inflammation, with some mice receiving a mouse TF-blocking antibody (muTF-Ab). The adhesion of leukocytes and platelets in colonic venules, light/dye-induced thrombus formation in cremaster muscle microvessels, as well as disease activity index, thrombin–antithrombin (TAT) complexes in plasma, and histopathologic changes in the colonic mucosa were monitored in untreated and muTF-Ab–treated colitic mice. In untreated mice, DSS elicited the recruitment of adherent leukocytes and platelets in colonic venules, caused gross and histologic injury, increased plasma TAT complexes, and enhanced thrombus formation in muscle arterioles. muTF-Ab prevented elevation in TAT complexes, reduced blood cell recruitment and tissue injury, and blunted thrombus formation in DSS colitic mice. These findings implicate TF in intestinal inflammation and support an interaction between inflammation and coagulation in experimental colitis

Role of Coagulation Factors in Cerebral Venous Sinus and Cerebral Microvascular Thrombosis

Thrombus formation can occur in both macroscopic and microscopic blood vessels. In the brain, cerebral venous sinus thrombosis (CVST) and focal cortical infarctions can result from the formation of thrombi in these different sized vessels. In this study we define the relative contributions of three major pro- and anti-coagulation pathways (heparin-antithrombin, protein C, and tissue factor (TF)) in the thrombogenic responses that occur in large and small vessels of the brain

Excess of heme induces tissue factor-dependent activation of coagulation in mice

An excess of free heme is present in the blood during many types of hemolytic anemia. This has been linked to organ damage caused by heme-mediated oxidative stress and vascular inflammation. We investigated the mechanism of heme-induced coagulation activation in vivo. Heme caused coagulation activation in wild-type mice that was attenuated by an anti-tissue factor antibody and in mice expressing low levels of tissue factor. In contrast, neither factor XI deletion nor inhibition of factor XIIa-mediated factor XI activation reduced heme-induced coagulation activation, suggesting that the intrinsic coagulation pathway is not involved. We investigated the source of tissue factor in heme-induced coagulation activation. Heme increased the procoagulant activity of mouse macrophages and human PBMCs. Tissue factor-positive staining was observed on leukocytes isolated from the blood of heme-treated mice but not on endothelial cells in the lungs. Furthermore, heme increased vascular permeability in the mouse lungs, kidney and heart. Deletion of tissue factor from either myeloid cells, hematopoietic or endothelial cells, or inhibition of tissue factor expressed by non-hematopoietic cells did not reduce heme-induced coagulation activation. However, heme-induced activation of coagulation was abolished when both non-hematopoietic and hematopoietic cell tissue factor was inhibited. Finally, we demonstrated that coagulation activation was partially attenuated in sickle cell mice treated with recombinant hemopexin to neutralize free heme. Our results indicate that heme promotes tissue factor-dependent coagulation activation and induces tissue factor expression on leukocytes in vivo. We also demonstrated that free heme may contribute to thrombin generation in a mouse model of sickle cell disease

Myeloid Cell Tissue Factor Does Not Contribute to Venous Thrombogenesis in an Electolytic Injury Model

Tissue factor (TF) is a potent initiator of the extrinsic coagulation cascade. The role and source of TF in venous thrombotic disease is not clearly defined. Our study objective was to identify the contribution of myeloid cell TF to venous thrombogenesis in mice

A Novel and Selective Dopamine Transporter Inhibitor, (S)-MK-26, Promotes Hippocampal Synaptic Plasticity and Restores Effort-Related Motivational Dysfunctions

Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson's and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of (S)-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered (S)-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, (S)-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, (S)-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight (S)-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for (S)-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders

Inflammation drives thrombosis after Salmonella infection via CLEC-2 on platelets

Thrombosis is a common, life-threatening consequence of systemic infection; however, the underlying mechanisms that drive the formation of infection-associated thrombi are poorly understood. Here, using a mouse model of systemic Salmonella Typhimurium infection, we determined that inflammation in tissues triggers thrombosis within vessels via ligation of C-type lectin-like receptor-2 (CLEC-2) on platelets by podoplanin exposed to the vasculature following breaching of the vessel wall. During infection, mice developed thrombi that persisted for weeks within the liver. Bacteria triggered but did not maintain this process, as thrombosis peaked at times when bacteremia was absent and bacteria in tissues were reduced by more than 90% from their peak levels. Thrombus development was triggered by an innate, TLR4-dependent inflammatory cascade that was independent of classical glycoprotein VI-mediated (GPVI-mediated) platelet activation. After infection, IFN-ã release enhanced the number of podoplanin-expressing monocytes and Kupffer cells in the hepatic parenchyma and perivascular sites and absence of TLR4, IFN-ã, or depletion of monocytic-lineage cells or CLEC-2 on platelets markedly inhibited the process. Together, our data indicate that infection-driven thrombosis follows local inflammation and upregulation of podoplanin and platelet activation. The identification of this pathway offers potential therapeutic opportunities to control the devastating consequences of infection-driven thrombosis without increasing the risk of bleeding