Oxygenated Nanocellulose-A Material Platform for Antibacterial Wound Dressing Devices.

Both carboxylated cellulose nanofibrils (CNF) and dissolved oxygen (DO) have been reported to possess antibacterial properties. However, the combination for use as wound dressings against biofilm infections in chronic wounds is less known. The present study reports the development of oxygenated CNF dispersions that exhibit strong antibacterial effect. Carboxylated CNF dispersions with different oxidation levels were oxygenated by the OXY BIO System and tested for antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus. The results reveal that the higher oxidation level of the CNFs, the better antibacterial effect. Scanning electron microscopy of bacterial biofilms revealed that a potential mechanism of action of the CNFs is the formation of a network surrounding and entrapping the bacteria. This effect is further potentiated by the oxygenation process. A CNF sample (concentration 0.6 wt %) that was oxygenated to a DO level of 46.4 mg/L demonstrated a strong antibacterial effect against S. aureusin vivo using a mouse model of surgical site infection. The oxygenated CNF dispersion reduced the bacterial survival by 71%, after 24 h treatment. The potent antibacterial effect indicates that oxygenated nanocellulose is a promising material for antibacterial wound dressings.

Effect of Drinking Oxygenated Water Assessed by in vivo MRI Relaxometry.

GRANT SUPPORT: This project was funded by the Research Council of Norway. BACKGROUND: Oxygen uptake through the gastrointestinal tract after oral administration of oxygenated water in humans is not well studied and is debated in the literature. Due to the paramagnetic properties of oxygen and deoxyhemoglobin, MRI as a technique might be able to detect changes in relaxometry values caused by increased oxygen levels in the blood. PURPOSE: To assess whether oxygen dissolved in water is absorbed from the gastrointestinal tract and transported into the bloodstream after oral administration. STUDY TYPE: A randomized, double-blinded, placebo-controlled crossover trial. POPULATION/SUBJECTS: Thirty healthy male volunteers age 20-35. FIELD STRENGTH/SEQUENCE: 3T/Modified Look-Locker inversion recovery (MOLLI) T1 -mapping and multi fast field echo (mFFE) T2 *-mapping. ASSESSMENT: Each volunteer was scanned in two separate sessions. T1 and T2 * maps were acquired repeatedly covering the hepatic portal vein (HPV) and vena cava inferior (VCI, control vein) before and after intake of oxygenated or control water. Assessments were done by placing a region of interest in the HPV and VCI. STATISTICAL TEST: A mixed linear model was performed to the compare control vs. oxygen group. RESULTS: Drinking caused a mean 1.6% 95% CI (1.1-2.0% P < 0.001) increase in T1 of HPV blood and water oxygenation attributed another 0.70% 95% confidence interval (CI) (0.07-1.3% P = 0.028) increase. Oxygenation did not change T1 in VCI blood. Mean T2 * increased 9.6% 95% CI (1.7-17.5% P = 0.017) after ingestion of oxygenated water and 1.2% 95% CI (-4.3-6.8% P = 0.661) after ingestion of control water. The corresponding changes in VCI blood were not significant. DATA CONCLUSION: Ingestion of water caused changes in T1 and T2 * of HPV blood compatible with dilution due to water absorption. The effects were enhanced by oxygen. Assessment of oxygen enrichment of HPV blood was not possible due to the dilution effect. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 2 J. Magn. Reson. Imaging 2020;52:720-728.

Determination of oxygen r1 at 3 Tesla using samples with a concentration range of dissolved oxygen.

OBJECTIVE: To investigate the sensitivity of modified Look-Locker inversion recovery (MOLLI) to measure changes in dissolved oxygen (DO) concentrations in water samples and to calculate sequence-specific relaxivity (r1m) and limit of detection (LOD). MATERIALS AND METHODS: Ten water samples with a range of DO concentrations were scanned at 3 T using two variations of MOLLI schemes. Using linear regression the r1 of DO was estimated from the measured DO concentrations and T1 relaxation rates (R1). The results were combined with previously reported values on in vivo stability measures of the MOLLI sequences and used to estimate a LOD. RESULTS: DO concentrations ranged from 0.5 to 21.6 mg L-1. A linear correlation between DO and R1 was obtained with both MOLLI sequences, with an average correlation coefficient (R2) 0.9 and an average estimated r1 ([Formula: see text]) of 4.45 × 10-3 s-1 mg-1 L. Estimated LOD was ≈ 10 mg L-1. CONCLUSION: MOLLI T1-mapping sequences may be used for detecting dissolved oxygen in vivo at 3 T with an [Formula: see text] in the range 4.18-4.8 × 10-3 s-1 mg-1 L and a corresponding LOD for dissolved oxygen of approximately 10 mg L-1. MOLLI-based T1 mapping may be a useful non-invasive tool for quantification of in vivo changes of DO concentration during oxygen challenges.

Precision of T1-relaxation time measurements in the hepatic portal vein: influence of measurement technique and sequence parameters.

OBJECTIVE: To investigate the effects of a range of parameter settings on T1 measurement stability in the portal vein using the T1-mapping sequences Look-Locker (LL) and Modified Look-Locker inversion recovery (MOLLI). MATERIALS AND METHODS: Ten different versions of LL and MOLLI sequences were tested and compared to a reference sequence provided by the MR manufacturer. Ten healthy volunteers were imaged multiple times on two separate scan days at 3T. The mean T1 values and coefficient of variation (CoV) were calculated for each of the ten sequences and compared to the reference sequence. RESULTS: Six of the tested sequences had T1 values close to the reference sequence; among those, three sequences achieved lower CoV than the reference sequence. Lowest CoV was achieved using a non-triggered LL sequence with 5 beat readout and a 45o flip angle (mean T1 1733 ms ± 89 ms, CoV 1.3% ± 0.58%). CONCLUSION: T1-measurements in the hepatic portal vein can be performed with high precision using either MOLLI or LL sequences provided that LL sampling duration is sufficiently long and flip angle sufficiently high. The advantage of constant timing outweighed the advantage of ECG-triggering.

Development of a novel in situ gelling skin dressing: Delivering high levels of dissolved oxygen at pH 5.5.

BACKGROUND AND AIMS: Wound healing requires appropriate oxygen and pH levels. Oxygen therapy and pH-modulating treatments have shown positive effects on wound healing. Thus, a dressing, which combines high levels of dissolved oxygen (DO) with the pH of intact skin, may improve wound healing. Our aims were to (1) formulate an in situ gelling dressing with high levels of DO and with the pH level of intact skin, (2) evaluate physical and chemical properties of the dressing, and (3) elucidate basic effects of elevated levels of DO on human skin cells in vitro. METHODS: A dressing was formulated with 15 to 16 wt% poloxamer 407, acetate buffer, and oxygenated water. Stability of pH and DO, rheology, and shelf life were analysed. Furthermore, in vitro studies of the effect of increased levels of DO were performed. RESULTS: An in situ gelling wound dressing, with a DO concentration ranging between 25 and 35 mg/L and a pH of 5.5, was formulated. The DO concentration was stable above 22 mg/L for at least 30 hours when applied on a surface at 35°C and covered for directed diffusion into the intended wound area. At storage, the dressing had stable pH for 3 months and stable DO concentration over 30 mg/L for 7 weeks. Increasing DO significantly enhanced intracellular ATP in human skin cells, without changing reactive oxygen species production, proliferation rate, or viability. CONCLUSION: The developed dressing may facilitate wound healing by delivering controlled and stable oxygen levels, providing adjustable pH for optimized healing, and increasing intracellular ATP availability.

The role of pannexin hemichannels in the anoxic depolarization of hippocampal pyramidal cells.

Neuronal gap junctional hemichannels, composed of pannexin-1 subunits, have been suggested to play a crucial role in epilepsy and brain ischaemia. After a few minutes of anoxia or ischaemia, neurons in brain slices show a rapid depolarization to ∼-20 mV, called the anoxic depolarization. Glutamate receptor blockers can prevent the anoxic depolarization, suggesting that it is produced by a cation influx through glutamate-gated channels. However, in isolated hippocampal pyramidal cells, simulated ischaemia evokes a large inward current and an increase in permeability to large molecules, mediated by the opening of pannexin-1 hemichannels. N-methyl-d-aspartate is also reported to open these hemichannels, suggesting that the activation of N-methyl-d-aspartate receptors, which occurs when glutamate is released in ischaemia, might cause the anoxic depolarization by evoking a secondary ion flux through pannexin-1 hemichannels. We tested the contribution of pannexin hemichannels to the anoxic depolarization in CA1 pyramidal cells in the more physiological environment of hippocampal slices. Three independent inhibitors of hemichannels-carbenoxolone, lanthanum and mefloquine-had no significant effect on the current generating the anoxic depolarization, while a cocktail of glutamate and gamma-aminobutyric acid class A receptor blockers abolished it. We conclude that pannexin hemichannels do not generate the large inward current that underlies the anoxic depolarization. Glutamate receptor channels remain the main candidate for generating the large inward current that produces the anoxic depolarization.

System A transporter SAT2 mediates replenishment of dendritic glutamate pools controlling retrograde signaling by glutamate.

Glutamate mediates several modes of neurotransmission in the central nervous system including recently discovered retrograde signaling from neuronal dendrites. We have previously identified the system N transporter SN1 as being responsible for glutamine efflux from astroglia and proposed a system A transporter (SAT) in subsequent transport of glutamine into neurons for neurotransmitter regeneration. Here, we demonstrate that SAT2 expression is primarily confined to glutamatergic neurons in many brain regions with SAT2 being predominantly targeted to the somatodendritic compartments in these neurons. SAT2 containing dendrites accumulate high levels of glutamine. Upon electrical stimulation in vivo and depolarization in vitro, glutamine is readily converted to glutamate in activated dendritic subsegments, suggesting that glutamine sustains release of the excitatory neurotransmitter via exocytosis from dendrites. The system A inhibitor MeAIB (alpha-methylamino-iso-butyric acid) reduces neuronal uptake of glutamine with concomitant reduction in intracellular glutamate concentrations, indicating that SAT2-mediated glutamine uptake can be a prerequisite for the formation of glutamate. Furthermore, MeAIB inhibited retrograde signaling from pyramidal cells in layer 2/3 of the neocortex by suppressing inhibitory inputs from fast-spiking interneurons. In summary, we demonstrate that SAT2 maintains a key metabolic glutamine/glutamate balance underpinning retrograde signaling by dendritic release of the neurotransmitter glutamate.

Vesicular release of glutamate from hippocampal neurons in culture: an immunocytochemical assay.

Glutamate, the main excitatory neurotransmitter in the brain, may cause excitotoxic damage through excessive release during a number of pathological conditions. We have developed an immunocytochemical assay to investigate the mechanisms and regulation of glutamate release from intact, cultured neurons. Our results indicate that cultured hippocampal neurons have a large surplus of glutamate available for release upon chemically induced depolarization. Long incubations with high K(+)-concentrations, and induction of repetitive action potentials with the K(+)-channel blocker 4-aminopyridine (4-AP), caused a significant reduction in glutamate labeling in a subset of boutons, demonstrating that transmitter release exceeded the capacity for replenishment. The number of boutons where release exceeded replenishment increased continuously with time of stimulation. This depletion was Ca(2+)-dependent and sensitive to bafilomycin A1 (baf), indicating that it was dominated by vesicular release mechanisms. The depletion of glutamate from cell bodies and dendrites was also Ca(2+)-dependent. Thus, under the present conditions, cytosolic glutamate is taken up in vesicles prior to release, and the main escape route for the amino acid is through vesicular exocytosis. Depolarization with lower concentrations of K(+) caused sustainable release of glutamate, i.e., without full depletion.

Ultrastructural localisation and differential agonist-induced regulation of AMPA and kainate receptors present at the presynaptic active zone and postsynaptic density.

Activity-dependent changes in ionotropic glutamate receptors at the postsynaptic membrane are well established and this regulation plays a central role in the expression of synaptic plasticity. However, very little is known about the distributions and regulation of ionotropic receptors at presynaptic sites. To determine if presynaptic receptors are subject to similar regulatory processes we investigated the localisation and modulation of AMPA (GluR1, GluR2, GluR3) and kainate (GluR6/7, KA2) receptor subunits by ultrasynaptic separation and immunoblot analysis of rat brain synaptosomes. All of the subunits were enriched in the postsynaptic fraction but were also present in the presynaptic and non-synaptic synaptosome fractions. AMPA stimulation resulted in a marked decrease in postsynaptic GluR2 and GluR3 subunits, but an increase in GluR6/7. Conversely, GluR2 and GluR3 increased in the presynaptic fraction whereas GluR6/7 decreased. There were no significant changes in any of the compartments for GluR1. NMDA treatment decreased postsynaptic GluR1, GluR2 and GluR6/7 but increased presynaptic levels of these subunits. NMDA treatment did not evoke changes in GluR3 localisation. Our results demonstrate that presynaptic and postsynaptic subunits are regulated in opposite directions by AMPA and NMDA stimulation.