Papers and References

Molecular hydrogen as a novel antioxidant: Overview of the advantages of hydrogen for medical applications

O (2015), Methods in Enzymology, vol. 555, 289 - 317
Molecular hydrogen (H2) was believed to be inert and nonfunctional in mammalian cells. We overturned this concept by demonstrating that H2reacts with highly reactive oxidants such as hydroxyl radical (•OH) and peroxynitrite (ONOO-) inside cells. H2has several advantages exhibiting marked effects for medical applications: it is mild enough neither to disturb metabolic redox reactions nor to affect signaling by reactive oxygen species. Therefore, it should have no or little adverse effects. H2can be monitored with an H2-specific electrode or by gas chromatography. H2rapidly diffuses into tissues and cells to exhibit efficient effects. Thus, we proposed the potential of H2for preventive and therapeutic applications. There are several methods to ingest or consume H2: inhaling H2gas, drinking H2-dissolved water (H2-water), injecting H2-dissolved saline (H2-saline), taking an H2bath, or dropping H2-saline onto the eyes. Recent publications revealed that, in addition to the direct neutralization of highly reactive oxidants, H2indirectly reduces oxidative stress by regulating the expression of various genes. Moreover, by regulating gene expression, H2functions as an anti-inflammatory, antiallergic, and antiapoptotic molecule, and stimulates energy metabolism. In addition to growing evidence obtained by model animal experiments, extensive clinical examinations were performed or are under way. Since most drugs specifically act on their specific targets, H2seems to differ from conventional pharmaceutical drugs. Owing to its great efficacy and lack of adverse effects, H2has potential for clinical applications for many diseases.

Diabetic Coma in Young Diabetics

O (1941), British Medical Journal, vol. 2, 30 -
Relationships among fluid flow, sulfide concentration, sulfur bacteria and macrofaunal assemblages were examined at methane seeps on the northern California margin, near the mouth of the Eel River (512 to 525 m). Over a 6 mo period, sediments covered with microbial mats exhibitedsignificant but variable outflow of altered fluids, with no flow reversals. This fluid flow was associated with high porewater sulfide concentrations (up to 20 mM) and almost no oxygen penetration of sediments (<0.1 mm). Vesicomya pacifica (clam) bed and non-seep sediments exhibited little net fluid outflow and similar oxygen penetration (3 and 4 mm, respectively); however, sulfide concentrations were higher in subsurface clam-bed sediments (up to 2 mM) than in non-seep sediments (<200 ìM). Macrofaunal densities did not differ among the 3 habitats (13 800 to 16 800 ind. m-2; >300 ìm), but biomass and diversity (no. species per core, E(S100), H') were lower and composition varied in the sulfidic microbial mat sediments relative to clam-bed and non-seep sediments. The community in microbial mat-covered sediments consisted largely (82%) of 6 species in the polychaete family Dorvilleidae, whereas the clam-bed and non-seep microhabitats supported a mixture of annelids, peracarid crustaceans, nemerteans, and mollusks. Vertical microprofiling of sulfide in animal cores indicated that most taxa avoid H2S concentrations >1 mM. However, sulfide-oxidizing filamentous bacteria, dorvilleid polychaetes and bivalves (mainly V. pacifica) exhibited highest densities at sulfide concentrations of 1 to 5 mM sulfide. Horizontal and vertical patterns of sulfide availability have a strong influence on the fine-scale distribution, structure and composition of macrofaunal assemblages inhabiting methane seeps and must be accounted for when characterizing the microbiology and ecology of seep habitats.

Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems

O'Connor, Ben L., Harvey, Judson W. (2008), Water Resources Research, vol. 44, 1 - 17
Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law generated by flow and bed topography at the sediment-water interface. However, many modes of transport are potentially involved (molecular diffusion, bioturbation, advection, shear, bed mobility, and turbulence) with even simple models being difficult to apply in complex natural systems characterized by variable sediment sizes and irregular bed geometries. In this study, we synthesize information from published hyporheic exchange investigations to develop a scaling relationship for estimating mass transfer in near-surface sediments across a range in fluid-flow and sediment conditions. Net hyporheic exchange was quantified using an effective diffusion coefficient (D e ) that integrates all of the various transport processes that occur simultaneously in sediments, and dimensional analysis was used to scale D e to shear stress velocity, roughness height, and permeability that describe fluid-flow and sediment characteristics. We demonstrated the value of the derived scaling relationship by using it to quantify dissolved oxygen (DO) uptake rates on the basis of DO profiles in sediments and compared them to independent flux measurements. The results support a broad application of the D e scaling relationship for quantifying coupled hyporheic exchange and biogeochemical reaction rates in streams and other aquatic ecosystems characterized by complex fluid-flow and sediment conditions.

Dissolved oxygen transfer to sediments by sweep and eject motions in aquatic environments

O'Connor, Ben L., Hondzo, Miki (2008), Limnology and Oceanography, vol. 53, 566 - 578
Dissolved oxygen (DO) concentrations were quantified near the sediment-water interface to evaluate DO transfer to sediments in a laboratory recirculating flume and open channel under varying fluid-flow conditions. DO concentration fluctuations were observed within the diffusive sublayer, as defined by the time-averaged DO concentration gradient near the sediment-water interface. Evaluation of the DO concentration fluctuations along with detailed fluid-flow characterizations were used to quantify quasi-periodic sweep and eject motions (bursting events) near the sediments. Bursting events dominated the Reynolds shear stresses responsible for momentum and mass fluctuations near the sediment bed. Two independent methods for detecting bursting events using DO concentration and velocity data produced consistent results. The average time between bursting events was scaled with wall variables and was incorporated into a similarity model to describe the dimensionless mass transfer coefficient (Sherwood number, Sh) in terms of the Reynolds number, Re, and Schmidt number, Sc, which described transport in the flow. The scaling of bursting events was employed with the similarity model to quantify DO transfer to sediments and results showed a high degree of agreement with experimental data.

Renal medullary tissue oxygenation is dependent on both cortical and medullary blood flow

O'Connor, P M, Kett, M M, Anderson, W P, Evans, R G (2006), Am J Physiol Renal Physiol, vol. 290, F688 - 94
The aim of the current study was to determine whether renal medullary oxygenation is independent of the level of cortical blood flow by testing responses to stimuli that selectively reduce blood flow in either the cortex or medulla. In anesthetized rabbits, renal arterial infusion of [Phe(2),Ile(3),Orn(8)]-vasopressin selectively reduced medullary perfusion and Po(2) (-54 +/- 24 and -50 +/- 10%, respectively) but did not significantly affect cortical perfusion or tissue oxygenation. In contrast, stimulation of the renal nerves resulted in renal cortical ischemia with reductions in total renal blood flow (-76 +/- 3% at 4 Hz), cortical perfusion (-57 +/- 17%), and cortical Po(2) (-44 +/- 12%). Medullary tissue Po(2) was reduced by -70 +/- 5% at 4 Hz, despite medullary perfusion being unaffected and distal tubular sodium reabsorption being reduced (by -83.3 +/- 1.2% from baseline). In anesthetized rats, in which renal perfusion pressure was maintained with an aortic constrictor, intravenous infusion of ANG II (0.5-5 microg. kg(-1).min(-1)) dose dependently reduced cortical perfusion (up to -65 +/- 3%; P < 0.001) and cortical Po(2) (up to -57 +/- 4%; P < 0.05). However, medullary perfusion was only significantly reduced at the highest dose (5 microg. kg(-1).min(-1); by 29 +/- 6%). Medullary perfusion was not reduced by 1 microg. kg(-1).min(-1) ANG II, but medullary Po(2) was significantly reduced (-12 +/- 4%). Thus, although cortical and medullary blood flow may be independently regulated, medullary oxygenation may be compromised during moderate to severe cortical ischemia even when medullary blood flow is maintained.

Acute SGLT inhibition normalizes O ₂ tension in the renal cortex but causes hypoxia in the renal medulla in anaesthetized control and diabetic rats

O'Neill, Julie, Fasching, Angelica, Pihl, Liselotte, Patinha, Daniela, Franzén, Stephanie, Palm, Fredrik (2015), American Journal of Physiology - Renal Physiology, vol. 309, F227 - F234
Early stage diabetic nephropathy is characterized by glomerular hyperfiltration and reduced renal tissue Po2. Recent observations have indicated that increased tubular Na+-glucose linked transport (SGLT) plays a role in the development of diabetes-induced hyperfiltration. The aim of the present study was to determine how inhibition of SLGT impacts upon Po2 in the diabetic rat kidney. Diabetes was induced by streptozotocin in Sprague-Dawley rats 2 wk before experimentation. Renal hemodynamics, excretory function, and renal O2 homeostasis were measured in anesthetized control and diabetic rats during baseline and after acute SGLT inhibition using phlorizin (200 mg/kg ip). Baseline arterial pressure was similar in both groups and unaffected by SGLT inhibition. Diabetic animals displayed reduced baseline Po2 in both the cortex and medulla. SGLT inhibition improved cortical Po2 in the diabetic kidney, whereas it reduced medullary Po2 in both groups. SGLT inhibition reduced Na+ transport efficiency [tubular Na+ transport (TNa)/renal O2 consumption (Qo2)] in the control kidney, whereas the already reduced TNa/Qo2 in the diabetic kidney was unaffected by SGLT inhibition. In conclusion, these data demonstrate that when SGLT is inhibited, renal cortex Po2 in the diabetic rat kidney is normalized, which implies that increased proximal tubule transport contributes to the development of hypoxia in the diabetic kidney. The reduction in medullary Po2 in both control and diabetic kidneys during the inhibition of proximal Na+ reabsorption suggests the redistribution of active Na+ transport to less efficient nephron segments, such as the medullary thick ascending limb, which results in medullary hypoxia.

Acute SGLT inhibition normalizes O ₂ tension in the renal cortex but causes hypoxia in the renal medulla in anaesthetized control and diabetic rats

O'Neill, Julie, Fasching, Angelica, Pihl, Liselotte, Patinha, Daniela, Franzén, Stephanie, Palm, Fredrik (2015), American Journal of Physiology - Renal Physiology, vol. 309, F227 - F234
Early stage diabetic nephropathy is characterized by glomerular hyperfiltration and reduced renal tissue Po2. Recent observations have indicated that increased tubular Na+-glucose linked transport (SGLT) plays a role in the development of diabetes-induced hyperfiltration. The aim of the present study was to determine how inhibition of SLGT impacts upon Po2 in the diabetic rat kidney. Diabetes was induced by streptozotocin in Sprague-Dawley rats 2 wk before experimentation. Renal hemodynamics, excretory function, and renal O2 homeostasis were measured in anesthetized control and diabetic rats during baseline and after acute SGLT inhibition using phlorizin (200 mg/kg ip). Baseline arterial pressure was similar in both groups and unaffected by SGLT inhibition. Diabetic animals displayed reduced baseline Po2 in both the cortex and medulla. SGLT inhibition improved cortical Po2 in the diabetic kidney, whereas it reduced medullary Po2 in both groups. SGLT inhibition reduced Na+ transport efficiency [tubular Na+ transport (TNa)/renal O2 consumption (Qo2)] in the control kidney, whereas the already reduced TNa/Qo2 in the diabetic kidney was unaffected by SGLT inhibition. In conclusion, these data demonstrate that when SGLT is inhibited, renal cortex Po2 in the diabetic rat kidney is normalized, which implies that increased proximal tubule transport contributes to the development of hypoxia in the diabetic kidney. The reduction in medullary Po2 in both control and diabetic kidneys during the inhibition of proximal Na+ reabsorption suggests the redistribution of active Na+ transport to less efficient nephron segments, such as the medullary thick ascending limb, which results in medullary hypoxia.

Probabilistic Invasion Underlies Natural Gut Microbiome Stability

Obadia, Benjamin, Güvener, Z. T., Zhang, Vivian, Ceja-Navarro, Javier A., Brodie, Eoin L., Ja, William W., Ludington, William B. (2017), Current Biology, vol. 27, 1999 - 2006.e8
Species compositions of gut microbiomes impact host health [1–3], but the processes determining these compositions are largely unknown. An unexplained observation is that gut species composition varies widely between individuals but is largely stable over time within individuals [4, 5]. Stochastic factors during establishment may drive these alternative stable states (colonized versus non-colonized) [6, 7], which can influence susceptibility to pathogens, such as Clostridium difficile. Here we sought to quantify and model the dose response, dynamics, and stability of bacterial colonization in the fruit fly (Drosophila melanogaster) gut. Our precise, high-throughput technique revealed stable between-host variation in colonization when individual germ-free flies were fed their own natural commensals (including the probiotic Lactobacillus plantarum). Some flies were colonized while others remained germ-free even at extremely high bacterial doses. Thus, alternative stable states of colonization exist even in this low-complexity model of host-microbe interactions. These alternative states are driven by a fundamental asymmetry between the inoculum population and the stably colonized population that is mediated by spatial localization and a population bottleneck, which makes stochastic effects important by lowering the effective population size. Prior colonization with other bacteria reduced the chances of subsequent colonization, thus increasing the stability of higher-diversity guts. Therefore, stable gut diversity may be driven by inherently stochastic processes, which has important implications for combatting infectious diseases and for stably establishing probiotics in the gut.

No abstract available.

Activity-induced tissue oxygenation changes in rat cerebellar cortex: Interplay of postsynaptic activation and blood flow

Offenhauser, Nikolas, Thomsen, Kirsten, Caesar, Kirsten, Lauritzen, Martin (2005), Journal of Physiology, vol. 565, 279 - 294
Functional neuroimaging relies on the robust coupling between neuronal activity, metabolism and cerebral blood flow (CBF), but the physiological basis of the neuroimaging signals is still poorly understood. We examined the mechanisms of activity-dependent changes in tissue oxygenation in relation to variations in CBF responses and postsynaptic activity in rat cerebellar cortex. To increase synaptic activity we stimulated the monosynaptic, glutamatergic climbing fibres that excite Purkinje cells via AMPA receptors. We used local field potentials to indicate synaptic activity, and recorded tissue oxygen partial pressure (P(tiss,O2)) by polarographic microelectrodes, and CBF using laser-Doppler flowmetry. The disappearance rate of oxygen in the tissue increased linearly with synaptic activity. This indicated that, without a threshold, oxygen consumption increased as a linear function of synaptic activity. The reduction in P(tiss,O2) preceded the rise in CBF. The time integral (area) of the negative P(tiss,O2) response increased non-linearly showing saturation at high levels of synaptic activity, concomitant with a steep rise in CBF. This was accompanied by a positive change in P(tiss,O2). Neuronal nitric oxide synthase inhibition enhanced the initial negative P(tiss,O2) response ('dip'), while attenuating the evoked CBF increase and positive P(tiss,O2) response equally. This indicates that increases in CBF counteract activity-induced reductions in P(tiss,O2), and suggests the presence of a tissue oxygen reserve. The changes in P(tiss,O2) and CBF were strongly attenuated by AMPA receptor blockade. Our findings suggest an inverse relationship between negative P(tiss,O2) and CBF responses, and provide direct in vivo evidence for a tight coupling between activity in postsynaptic AMPA receptors and cerebellar oxygen consumption.

On the Mechanism of Polyamide Degradation in Chlorinated Water

Ogilby, P R, Dam, N (2001), Helvetica chimica acta, vol. 84, 2540 - 2549
| Ayuda. On the Mechanism of Degradation in Chlorinated Water. Autores: PR Ogilby, N. Dam; Localización: , ISSN 0018-019X, . , Nº 9, , pags. 2540-2549. © -2010 Universidad de La Rioja · Todos los derechos reservados.

Protection of the retina by rapid diffusion of hydrogen: Administration of hydrogen-loaded eye drops in retinal ischemia-reperfusion injury

Oharazawa, Hideaki, Igarashi, Tsutomu, Yokota, Takashi, Fujii, Hiroaki, Suzuki, Hisaharu, Machide, Mitsuru, Takahashi, Hiroshi, Ohta, Shigeo, Ohsawa, Ikuroh (2010), Investigative Ophthalmology and Visual Science, vol. 51, 487 - 492
PURPOSE: Retinal ischemia-reperfusion (I/R) injury by transient elevation of intraocular pressure (IOP) is known to induce neuronal damage through the generation of reactive oxygen species. Study results have indicated that molecular hydrogen (H(2)) is an efficient antioxidant gas that selectively reduces the hydroxyl radical (*OH) and suppresses oxidative stress-induced injury in several organs. This study was conducted to explore the neuroprotective effect of H(2)-loaded eye drops on retinal I/R injury. METHODS: Retinal ischemia was induced in rats by raising IOP for 60 minutes. H(2)-loaded eye drops were prepared by dissolving H(2) gas into a saline to saturated level and administered to the ocular surface continuously during the ischemia and/or reperfusion periods. One day after I/R injury, apoptotic cells in the retina were quantified, and oxidative stress was evaluated by markers such as 4-hydroxynonenal and 8-hydroxy-2-deoxyguanosine. Seven days after I/R injury, retinal damage was quantified by measuring the thickness of the retina. RESULTS: When H(2)-loaded eye drops were continuously administered, H(2) concentration in the vitreous body immediately increased and I/R-induced *OH level decreased. The drops reduced the number of retinal apoptotic and oxidative stress marker-positive cells and prevented retinal thinning with an accompanying activation of Müller glia, astrocytes, and microglia. The drops improved the recovery of retinal thickness by >70%. CONCLUSIONS: H(2) has no known toxic effects on the human body. Thus, the results suggest that H(2)-loaded eye drops are a highly useful neuroprotective and antioxidative therapeutic treatment for acute retinal I/R injury.

Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals

Ohsawa, Ikuroh, Ishikawa, Masahiro, Takahashi, Kumiko, Watanabe, Megumi, Nishimaki, Kiyomi, Yamagata, Kumi, Katsura, Ken Ichiro, Katayama, Yasuo, Asoh, Sadamitsu, Ohta, Shigeo (2007), Nature Medicine, vol. 13, 688 - 694
Acute oxidative stress induced by ischemia-reperfusion or inflammation causes serious damage to tissues, and persistent oxidative stress is accepted as one of the causes of many common diseases including cancer. We show here that hydrogen (H(2)) has potential as an antioxidant in preventive and therapeutic applications. We induced acute oxidative stress in cultured cells by three independent methods. H(2) selectively reduced the hydroxyl radical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H(2) did not react with other ROS, which possess physiological roles. We used an acute rat model in which oxidative stress damage was induced in the brain by focal ischemia and reperfusion. The inhalation of H(2) gas markedly suppressed brain injury by buffering the effects of oxidative stress. Thus H(2) can be used as an effective antioxidant therapy; owing to its ability to rapidly diffuse across membranes, it can reach and react with cytotoxic ROS and thus protect against oxidative damage.

Effect of nitrite and nitrate on biogenic sulfide production in sewer biofilms determined by the use of microelectrodes

Okabe, S., Ito, T., Satoh, H., Watanabe, Y. (2003), Water Science and Technology, vol. 47, 281 - 288
The effects of O2 and NO3- concentrations on in situ sulfate reduction and sulfide reoxidation in microaerophilic wastewater biofilms grown on rotating disk reactors were investigated by the use of microelectrodes for O2, S2-, NO3-, NO2-, and pH. Microelectrode measurements showed the vertical microzonation of O2 respiration, NO3- respiration, H2S oxidation and SO4(2-) reduction in the biofilms. The microelectrode measurements indicate that sulfate reducing activity was largely restricted to a narrow anaerobic zone located about 500 microm below the biofilm surface. An addition of nitrate forced the sulfate reduction zone deeper in the biofilm and reduced the specific sulfate reduction rate as well. The sulfate reduction zone was consequently separated from the O2 and NO3- respiration zones. Anaerobic H2S oxidation with NO3- was also induced by addition of nitrate to the medium. Measurements of the reduced inorganic sulfur compounds (FeS, FeS2 and S0), total-Mn and total-Fe in the biofilm indicated that the produced H2S became immediately oxidized with O2, NO3- and other oxidants, mainly ferric/ferrous hydrates. On the basis of the present results, it was estimated that of all sulfide produced, 13% of the sulfide was precipitated by metal ions as FeS and S0 just above the sulfate reduction zone, 65% was anaerobically oxidized to SO4(2-) with NO3- as an electron acceptor and 22% was aerobically oxidized within the biofilm incubated in 70 micromol l(-1) of DO and 280 micromol l(-1) of NO3-.

Analyses of spatial distributions of sulfate-reducing bacteria and their activity in aerobic wastewater biofilms

Okabe, Satoshi, Itoh, Tsukasa, Satoh, Hisashi, Watanabe, Yoshimasa (1999), Applied and Environmental Microbiology, vol. 65, 5107 - 5116
The vertical distribution of sulfate-reducing bacteria (SRB) in aerobic wastewater biofilms grown on rotating disk reactors was investigated by fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. To correlate the vertical distribution of SRB populations with their activity, the microprofiles of O(2), H(2)S, NO(2)(-), NO(3)(-), NH(4)(+), and pH were measured with microelectrodes. In addition, a cross-evaluation of the FISH and microelectrode analyses was performed by comparing them with culture-based approaches and biogeochemical measurements. In situ hybridization revealed that a relatively high abundance of the probe SRB385-stained cells (approximately 10(9) to 10(10) cells per cm(3) of biofilm) were evenly distributed throughout the biofilm, even in the oxic surface. The probe SRB660-stained Desulfobulbus spp. were found to be numerically important members of SRB populations (approximately 10(8) to 10(9) cells per cm(3)). The result of microelectrode measurements showed that a high sulfate-reducing activity was found in a narrow anaerobic zone located about 150 to 300 microm below the biofilm surface and above which an intensive sulfide oxidation zone was found. The biogeochemical measurements showed that elemental sulfur (S(0)) was an important intermediate of the sulfide reoxidation in such thin wastewater biofilms (approximately 1,500 microm), which accounted for about 75% of the total S pool in the biofilm. The contribution of an internal Fe-sulfur cycle to the overall sulfur cycle in aerobic wastewater biofilms was insignificant (less than 1%) due to the relatively high sulfate reduction rate.

Successional development of sulfate-reducing bacterial populations and their activities in an activated sludge immobilized agar gel film

Okabe, Satoshi, Santegoeds, Cecilia M., Watanabe, Yoshimasa, De Beer, Dirk (2002), Biotechnology and Bioengineering, vol. 78, 119 - 130
A combination of fluorescence in situ hybridization (FISH), microprofiles, and denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rDNA fragments followed by hybridization analysis with specific probes was applied to investigate successional development of sulfate-reducing bacteria (SRB) community structure and in situ sulfide production activity within an activated sludge immobilized agar gel film. In this model biofilm system, since biases arising from biofilm heterogeneity can be ignored, the population dynamics of SRB in the agar gel is directly related to physiological capability and in situ activity of SRB. Microelectrode measurements showed that an anoxic zone was already developed at the beginning (0 day), a first sulfide production of 0.054 mumol H2S m(-2) x s(-1) was detected during the first week, and the rate increased gradually to 0.221 mumol H2S m(-2) x s(-1) in the fifth week. The most active sulfide production zone moved upward to the chemocline and intensified with time to form a narrow zone with high volumetric sulfide production rates. This result coincided with the shift of the spatial distributions of SRB populations determined by FISH. In situ hybridization with probe SRB385 for mainly general SRB of the delta Proteobacteria plus some gram-positive bacteria and probe 660 for Desulfobulbus indicated that the most abundant populations of SRB were primarily restricted to near the oxic/anoxic interface (chemocline). A close observation of the development of the vertical distributions of SRB populations revealed that the cell numbers of Desulfobulbus tripled (from 0.5 x 10(8) to 1.5 x 10(8) cells cm(-3)) near the oxic/anoxic interface. Similar growth (from 1.0 x10(8) to 4.5 x 10(8) cells cm(-3)) of Desulfovibrio-like SRB that hybridized with probe SRB385 was observed. PCR-DGGE followed by hybridization analysis revealed that one Desulfobulbus strain was detected from the beginning, and another strain appeared after 1 week, coinciding with the first detected sulfide production. In addition, three strains hybridizing with probe 687 (possibly Desulfovibrio) were also dominant SRB in the agar gel.

No abstract available.

Expression of vascular endothelial growth factor receptor 1 in bone marrow-derived mesenchymal cells is dependent on hypoxia-inducible factor 1

Okuyama, Hiroaki, Krishnamachary, Balaji, Zhou, Yi Fu, Nagasawa, Hideko, Bosch-Marce, Marta, Semenza, Gregg L. (2006), Journal of Biological Chemistry, vol. 281, 15554 - 15563
Bone marrow-derived cells are recruited to sites of ischemia, where they promote tissue vascularization. This response is dependent upon the expression of vascular endothelial growth factor (VEGF) receptor 1 (VEGFR1), which mediates cell migration in response to VEGF or placental growth factor (PLGF). In this study, we found that exposure of cultured mouse bone marrow-derived mesenchymal stromal cells (MSC) to hypoxia or an adenovirus encoding a constitutively active form of hypoxia-inducible factor 1 (HIF-1) induced VEGFR1 mRNA and protein expression and promoted ex vivo migration in response to VEGF or PLGF. MSC in which HIF-1 activity was inhibited by a dominant negative or RNA interference approach expressed markedly reduced levels of VEGFR1 and failed to migrate or activate AKT in response to VEGF or PLGF. Thus, loss-of-function and gain-of-function approaches demonstrated that HIF-1 activity is necessary and sufficient for basal and hypoxia-induced VEGFR1 expression in bone marrow-derived MSC.

No abstract available.

Real-time quantification of microbial degradation of copepod fecal pellets monitored by isothermal microcalorimetry

Olsen, Søren N., Westh, Peter, Hansen, Benni W. (2005), Aquatic Microbial Ecology, vol. 40, 259 - 267
This study introduces isothermal microcalorimetry as a method to describe microbial degradation of copepod fecal pellets through measurements of the metabolic heat-flow produced by the degrading microbial community. We monitored the heat-flow for 20 to 24 h from samples of 300 to 1500 fecal pellets from a laboratory-cultivated calanoid copepod, Acartia tonsa Dana, fed on the chryptophyte Rhodomonas salina in excess. The microbes grew at 0.095 to 0.24 h(-1). Specific degradation rates were calculated using 3 different literature values of the carbon:volume ratio of fecal pellets. The mean +/- SD specific degradation rates, R-d, were estimated at 0.023 +/- 0.015 h(-1) (for carbon:volume ratio of 0.39 pg C mu m(-3)) and at 0.047 +/- 0.038 h(-1) (for carbon:volume ratio of 0.25 pg C mu m(-3)), defined as the proportion of fecal pellet carbon completely oxidised to CO2 h(-1). The lowest carbon:volume ratio (0.085 pgC mu m(-3)) resulted in >100% fecal pellet carbon degradation within 20 h. These degradation rates are very high, presumably reflecting a fully active bacterial population. The limiting factor for microbial growth was not inorganic nutrients (N and P), but labile dissolved organic carbon (DOC). We compared heat-flow in situations with and without oxygen, and found it to be 1 order of magnitude lower under anoxic conditions. This indicates the presence of anaerobic or facultative bacteria associated with the fecal pellets. Possible applications of the methodology are discussed.

Hydrogen sulfide as an oxygen sensor/transducer in vertebrate hypoxic vasoconstriction and hypoxic vasodilation

Olson, K. R., Dombkowski, R. A., Russell, M. J., Doellman, M. M., Head, S. K., Whitfield, N. L., Madden, J. A. (2006), Journal of Experimental Biology, vol. 209, 4011 - 4023
How vertebrate blood vessels sense acute hypoxia and respond either by constricting (hypoxic vasoconstriction) or dilating (hypoxic vasodilation) has not been resolved. In the present study we compared the mechanical and electrical responses of select blood vessels to hypoxia and H2S, measured vascular H2S production, and evaluated the effects of inhibitors of H2S synthesis and addition of the H2S precursor, cysteine, on hypoxic vasoconstriction and hypoxic vasodilation. We found that: (1) in all vertebrate vessels examined to date, hypoxia and H2S produce temporally and quantitatively identical responses even though the responses vary from constriction (lamprey dorsal aorta; lDA), to dilation (rat aorta; rA), to multi-phasic (rat and bovine pulmonary arteries; rPA and bPA, respectively). (2) The responses of lDA, rA and bPA to hypoxia and H2S appear competitive; in the presence of one stimulus, the response to the other stimulus is substantially or completely eliminated. (3) Hypoxia and H2S produce the same degree of cell depolarization in bPA. (4) H2S is constitutively synthesized by lDA and bPA vascular smooth muscle. (5) Inhibition of H2S synthesis inhibits the hypoxic response of lDA, rA, rPA and bPA. (6) Addition of the H2S precursor, cysteine, doubles hypoxic contraction in lDA, prolongs contraction in bPA and alters the re-oxygenation response of rA. These studies suggest that H2S may serve as an O2 sensor/transducer in the vascular responses to hypoxia. In this model, the concentration of vasoactive H2S in the vessel is governed by the balance between endogenous H2S production and its oxidation by available O2.

Better vascular engraftment and function in pancreatic islets transplanted without prior culture

Olsson, R., Carlsson, P. O. (2005), Diabetologia, vol. 48, 469 - 476
AIMS/HYPOTHESIS: Recent studies suggest that donor endothelial cells may contribute to islet graft revascularisation. Since islet endothelial cells disappear during culture, we hypothesised that transplantation of islets without prior culture is beneficial for their engraftment. METHODS: Cultured (4-7 days) or freshly isolated islets (<4 h after donor pancreas extirpation) were syngeneically transplanted into Wistar-Furth rats and C57Bl/6 mice beneath the renal capsule. Islet graft revascularisation was evaluated by measuring vascular density, blood flow and tissue oxygen tension. Islet graft function was investigated by a minimal islet mass model in inbred mice (C57Bl/6). RESULTS: Four days after implantation, the partial pressure of oxygen (pO2) in the transplanted cultured islets was less than 10 mmHg (1.33 kPa), but tended to be higher in grafts composed of freshly isolated islets. The pO2 in the grafts of freshly isolated islets had more than doubled 4 weeks later, whereas the pO2 in the grafts of cultured islets remained at values similar to those recorded 4 days after transplantation. Transplanted freshly isolated islets also had a higher vascular density than transplanted cultured islets (approximately 40 vs approximately 25% of that in endogenous islets) when investigated 1 month post-implantation. When applying a minimal islet mass model in inbred mice, 200 freshly isolated islets cured alloxan-diabetic mice in all cases, whereas only 33% of the group receiving similar numbers of cultured islets were cured. CONCLUSIONS/INTERPRETATION: Transplantation of pancreatic islets without prior culture is beneficial for their vascular engraftment and function.

Revascularization of transplanted pancreatic islets following culture with stimulators of angiogenesis

Olsson, Richard, Maxhuni, Arber, Carlsson, Per Ola (2006), Transplantation, vol. 82, 340 - 347
BACKGROUND: Insufficient revascularization of transplanted islets may result in chronic hypoxia and loss of islet function. This study investigated whether simple culture of islets with angiogenic substances before transplantation could improve graft revascularization. METHODS: Mouse islets were cultured with vascular endothelial growth factor (VEGF; 20 ng/ml), fibroblast growth factor 2 (FGF-2; 20 ng/ml) or matrix metalloproteinase 9 (MMP-9; 1 mug/ml). Thereafter, 250 islets were implanted beneath the renal capsule of syngeneic C57Bl/6 mice. One month posttransplantation, blood flow (laser-Doppler flowmetry), oxygen tension (Clark microelectrodes), and vascular density were measured and correlated to graft function. RESULTS: Treatment of islets with VEGF during culture caused islet blood vessels to dilate, whereas FGF-2 treatment induced endothelial cell proliferation. However, the number of capillaries in both cases decreased during culture. When investigated one month posttransplantation, both VEGF and FGF-2 pretreated islets had similar or worse vascular engraftment when compared to transplanted control islets. MMP-9 pretreatment of islets increased vascular density, blood flow and oxygen tension within the grafts. Animals receiving MMP-9 pretreated islets returned, however, more slowly to normoglycemia than control animals, and performed worse than controls in a glucose tolerance test one month posttransplantation. CONCLUSIONS: Treatment of islets during culture with VEGF or FGF-2 changed the islet vascular phenotype, but capillaries were still lost. Notably, the number of capillaries in the grafted islets one month posttransplantation was in all cases strikingly similar to that observed prior to transplantation. MMP-9 pretreatment of islets elicited an angiogenic response, which improved revascularization of the transplanted islets.

Modeling the influence of benthic primary production on oxygen transport through the water-sediment interface

Ordoñez, César, de la Fuente, Alberto, Díaz-Palma, Paula (2015), Ecological Modelling, vol. 311, 1 - 10
The context of this study is salty lagoons a few centimeters deep that are found in the arid region of the Andes Mountains in South America. The trophic structure of these aquatic ecosystems is supported by microalgae and photosynthetic bacteria located in the upper part of the sediment, and wind is the primary driver of mass and momentum transport through the water-sediment interface (WSI). This study proposes and validates, based on laboratory experiments, a simple algebraic expression computing dissolved oxygen (DO) exchange through the WSI considering benthic primary production. The algebraic expression was derived by vertically integrating DO diffusion-reaction equation in sediments divided into two layers: the upper heterogeneous layer where photosynthesis occurs and the lower layer where DO is consumed by biochemical reactions. Experiments were conducted in a wind tunnel with a water tank of variable depth that was at the downwind end of the experimental facility. Fresh sediments were placed in the middle of the tank such that DO was both consumed and produced in the sediments. This particular setup provides the required experimental conditions to measure the diffusion flux through the WSI, as well as the rate of consumption and production in the sediment, based on DO microprofiles. Based on 48 samples, the theoretical expression to compute the DO flux through the WSI was successfully validated. This expression can be used for computing DO exchanges fluxes across the WSI in shallow water bodies, where benthic primary production releases DO to the water during the day, and DO is consumed during the night.

The "nutrient pump:" Iron-poor sediments fuel low nitrogen-to-phosphorus ratios and cyanobacterial blooms in polymictic lakes

Orihel, Diane M., Schindler, David W., Ballard, Nathaniel C., Graham, Mark D., O'Connell, David W., Wilson, Lindsey R., Vinebrooke, Rolf D. (2015), Limnology and Oceanography, vol. 60, 856 - 871
Several lines of evidence from a eutrophic lake show how polymixis enables phosphorus (P) released from anoxic, iron (Fe)-poor sediments to lower nitrogen-to-phosphorus (N : P) ratios and stimulate cyanobacterial blooms. Detailed sediment analyses revealed extensive formation of Fe sulfides, which suppressed porewater Fe levels and prevented sequestration of P in Fe minerals. Experimental additions of Fe significantly decreased the flux of dissolved P from warm, anoxic sediments, increasing N : P ratios in porewater and overlying water. The net midsummer effect of polymixis and P release from Fe-poor sediments quickly doubled the total P in the euphotic zone during a period of very low external P loading. This internal “nutrient pump” decreased N : P in surface waters and led to a cyanobacterial bloom comprised primarily of diazotrophic Anabaena and Aphanizomenon spp. along with nonheterocystous and potentially toxic Microcystis icthyoblabe and Woronichinia naegelianum. Concentrations of the cyanotoxin, microcystin, in this lake were typically elevated during, or shortly after, episodes of internal P loading. Our study demonstrates an important mechanism underlying the increasing cyanobacterial dominance of weakly stratified eutrophic north temperate lakes, and warns of further increases under a warming climate.

Experimental iron amendment suppresses toxic cyanobacteria in a hypereutrophic lake

Orihel, Diane M., Schindler, David W., Ballard, Nathaniel C., Wilson, Lindsey R., Vinebrooke, Rolf D. (2016), Ecological Applications, vol. 26, 1517 - 1534
The effects of reducing nutrient inputs to lakes and reservoirs are often delayed by hysteresis resulting from internal phosphorus (P) loading from sediments. Consequently, controlling harmful algal blooms (HABs) in many eutrophic ecosystems requires additional management to improve water quality. We manipulated iron (Fe) concentrations in a hypereutrophic lake to determine if Fe amendment would suppress HABs by inhibiting P release from sediments. Our experiment consisted of 15 in situ mesocosms: 12 of which each received a different dose of Fe (ranging from 2 to 225 g m-2), and the remaining three were unmanipulated to serve as controls. Iron amendment decreased P accumulation in porewaters and the flux of P from sediments, which significantly lowered P concentrations in the water column. Iron exerted significant dose-dependent negative effects on the biomass of phytoplankton and periphyton, and reduced the dominance of cyanobacteria. Even at the lowest doses, Fe appeared to reduce the toxicity of cyanobacterial blooms, as measured by concentrations of hepatotoxic microcystins. Overall, our findings highlight the potential for Fe treatment as an effective strategy for minimizing HABs in eutrophic lakes and reservoirs. More broadly, our study reinforces the importance of Fe in regulating the trophic state of freshwaters, and the sensitivity of certain ecosystems to changes in Fe supply. Finally, we hypothesize that decreases in natural Fe supplies to lakes associated with anthropogenic activities may worsen outbreaks of toxic cyanobacteria.

Oscillations in oxygen tension and insulin release of individual pancreatic ob/ob mouse islets

Ortsäter, H., Liss, P., Lund, P. E., Åkerman, K. E.O., Bergsten, P. (2000), Diabetologia, vol. 43, 1313 - 1318
AIMS/HYPOTHESIS: The role of beta-cell metabolism for generation of oscillatory insulin release was investigated by simultaneous measurements of oxygen tension (pO2) and insulin release from individual islets of Langerhans. METHODS: Individual islets isolated from the ob/ob-mice were perifused. Insulin in the perifusate was measured with a sensitive ELISA and PO2 with a modified Clark-type electrode inserted into the islets. RESULTS: In the presence of 3 mmol/l D-glucose, PO2 was 102 +/- 9 mmHg and oscillatory (0.26 +/- 0.04 oscillations/min). Corresponding insulin measurements showed oscillatory release with similar periodicity (0.25 +/- 0.02 oscillations/min). When the D-glucose concentration was increased to 11 mmol/l, PO2 decreased by 30% to 72 +/- 10 mmHg with maintained frequency of the oscillations. Corresponding insulin secretory rate rose from 5 +/- 2 to 131 +/- 16 pmol x g(-1) x s(-1) leaving the frequency of the insulin pulses unaffected. The magnitude of glucose-induced change in pO2 varied between islets but was positively correlated to the amount of insulin released (r2 = 0.85). When 1 mmol/l tolbutamide was added to the perifusion medium containing 11 mmol/l glucose no change in average oscillatory pO2 was observed despite a doubling in the secretory rate. When 8 mmol/l 3-oxymethyl glucose was added to perifusion medium containing 3 mmol/l D-glucose, neither pO2 nor insulin release of the islets were changed. Temporal analysis of oscillations in pO2 and insulin release revealed that maximum respiration correlated to maximum or close to maximum insulin release. CONCLUSION/INTERPRETATION: The temporal relation between oscillations in pO2 and insulin release supports a role for metabolic oscillations in the generation of pulsatile insulin release.

Changes in Nitrogen Cycling Processes Along a Salinity Gradient in Tidal Wetlands of the Hudson River, New York, USA

Osborne, Robert I., Bernot, Melody J., Findlay, Stuart E.G. (2015), Wetlands, vol. 35, 323 - 334
Rising sea levels and stronger storm surges may expose tidal freshwater wetlands to saline waters, possibly leading to increased sulfate reduction and higher sulfide (H2S) concentrations. To better understand the effects of salinity on nitrogen cycling, porewater chemistry and sediment profiles of H2S and dissolved oxygen (O2) were measured along a salinity gradient in the Hudson River (New York, USA). Additionally, laboratory experiments exposed freshwater sediments to varying salinities after which sediment O2 and H2S dynamics along with nitrification and denitrification were measured. Overall, sites with higher salinities had lower oxygen availability (both as concentration and oxic sediment depth) and higher sulfide concentrations. Both nitrification and denitrification were depressed at higher salinities suggesting that exposure to saline water may alter nitrogen cycling of tidally influenced wetlands in the brackish region of the Hudson River estuary which may result in reduced retention of nitrogen.

Hydroxylamine-dependent anaerobic ammonium oxidation (anammox) by "Candidatus Brocadia sinica"

Oshiki, Mamoru, Ali, Muhammad, Shinyako-Hata, Kaori, Satoh, Hisashi, Okabe, Satoshi (2016), Environmental microbiology, vol. 18, 3133 - 3143
Although metabolic pathways and associated enzymes of anaerobic ammonium oxidation (anam- mox) of ‘Ca. Kuenenia stuttgartiensis’ have been studied, those of other anammox bacteria are still poorly understood. NO2 2 reduction to NO is consid- ered to be the first step in the anammox metabolism of ‘Ca. K. stuttgartiensis’, however, ‘Ca. Brocadia’ lacks the genes that encode canonical NO-forming nitrite reductases (NirS or NirK) in its genome, which is different from ‘Ca. K. stuttgartiensis’. Here, we studied the anammox metabolism of ‘Ca. Brocadia sinica’. 15N-tracer experiments demonstrated that ‘Ca. B. sinica’ cells could reduce NO2 2 to NH2OH, instead of NO, with as yet unidentified nitrite reduc- tase(s). Furthermore, N2H4 synthesis, downstream reaction of NO2 2 reduction, was investigated using a purified ‘Ca. B. sinica’ hydrazine synthase (Hzs) and intact cells. Both the ‘Ca. B. sinica’ Hzs and cells uti- lized NH2OH and NH1 4 , but not NO and NH1 4 , for N2H4 synthesis and further oxidized N2H4 to N2 gas. Taken together, the metabolic pathway of ‘Ca. B. sinica’ is NH2OH-dependent and different from the one of ‘Ca. K. stuttgartiensis’, indicating metabolic diversity of anammox bacteria.

No abstract available.

No abstract available.

Observations on microbial activity in acidified pig slurry

Ottosen, Lars D.M., Poulsen, Henrik V., Nielsen, Daniel Aagren, Finster, Kai, Nielsen, Lars Peter, Revsbech, Niels Peter (2009), Biosystems Engineering, vol. 102, 291 - 297
Acidification of pig slurry to pH 5.5 is used as a measure to reduce ammonia emission from pits and storages. The slurry is acidified with sulphuric acid in a process tank and pumped back to the slurry pits or to a storage tank. We investigated the effect of acidification on microbial activity. Oxygen consumption rate, methanogenesis and sulphate reduction were all reduced by more than 98% in the stored acidified slurry compared to untreated slurry. Despite higher sulphate concentration, the microbial metabolism was greatly compromised or absent in the acidified slurry. This could be explained by the high concentration of protonized short-chained volatile fatty acids in the acidified slurry (approximately 25 mM, compared to untreated slurry <0.1 mM), which act as an uncoupling agent of the cell membrane potential and thereby arrest microbial metabolism. In total the consequences of slurry acidification are greatly reduced production rates and loss of sulphide and methane, and eliminated loss of ammonia. On the other hand, increased volatilization and loss of smelly fatty acids is to be expected. © 2008 IAgrE.

Hypoxia-induced relaxation of porcine retinal arterioles in vitro depends on inducible NO synthase and EP4 receptor stimulation in the perivascular retina

Oversø Hansen, Pernille, Kringelholt, Sidse, Simonsen, Ulf, Bek, Toke (2015), Acta Ophthalmologica, vol. 93, 457 - 463
Purpose Hypoxia-induced relaxation of porcine retinal arterioles has been shown to be reduced during inhibition of prostaglandin synthesis and nitric oxide synthase (NOS). The purpose of this study was to identity the specific prostaglandin receptor(s) and source(s) of NO mediating this effect. Methods Porcine retinal arterioles with preserved perivascular retinal tissue were mounted in a myograph and were exposed to hypoxia in the presence of one of the following: the general NO synthase inhibitor L-NAME, the selective iNOS inhibitor 1400W, the selective nNOS inhibitor 7-nitroindazole, the general cyclooxygenase (COX) inhibitor ibuprofen or an antagonist to the FP- (AL 8810), DP- (BWA868C), EP1- (SC-19220), EP2- (PF-044189) or EP4 receptors (GW627368X). The experiments were repeated after removal of the perivascular retinal tissue. Results Hypoxia induced relaxation of retinal arterioles with preserved perivascular retinal tissue. This relaxation was significantly reduced in the presence of L-NAME, 1400W, ibuprofen and the EP4 receptor antagonist GW627368X. The simultaneous addition of L-NAME or 1400W in combination with ibuprofen, but not GW627368X, reduced hypoxia-induced vasorelaxation additively as compared to the effect of the compounds individually. Conclusion Hypoxia-induced vasorelaxation of porcine retinal arterioles is mediated by inducible NOS and stimulation of EP4 receptors acting through separate pathways, but mechanisms unrelated to the studied prostaglandin receptors and NOS products are also involved.

No abstract available.