Spatial and temporal variability of methane emissions from cascading reservoirs in the Upper Mekong River.

Reservoirs are an important source of atmospheric methane (CH4), a potent greenhouse gas. The Mekong, one of the largest Asian rivers, has been heavily dammed and can be a potential hotspot for CH4 emissions. While low diffusive CH4 flux was previously reported from cascading reservoirs in the Upper Mekong, the contribution of ebullition (bubbling) remained unexplored. To better constrain the magnitude and drivers of ebullition from these reservoirs, automated bubble traps were deployed in four reservoirs, allowing for continuous measurement of the ebullitive flux with high temporal resolution for a period of six months. To characterize the spatial variability of CH4 fluxes mediated by ebullition and diffusion, whole-reservoir surveys were conducted using a scientific echo sounder for bubble observations together with a gas equilibrator for mapping dissolved CH4 concentration in surface water from which diffusive fluxes were estimated. Potential production and anaerobic oxidation rates of CH4 were estimated in laboratory incubations of sediment cores collected near the bubble trap deployment sites. The CH4 production potential in sediments increased strongly along the reservoir cascade, with mostly minor reduction by anaerobic oxidation. Surface CH4 fluxes, in contrast, showed high spatial variability in both ebullitive and diffusive pathways (ranging 0.05-44 and 1.8-6.4 mg m-2 d-1, respectively, among all reservoirs). Ebullitive fluxes were about one order of magnitude higher than diffusive fluxes and remained significant at sites as deep as 30-45 m. The repeated spatial pattern of ebullition (higher fluxes at the dam area than in upstream sections) suggests the possible control of emission rates by sediment transport and deposition.

Gene deficiency and pharmacological inhibition of caspase-1 confers resilience to chronic social defeat stress via regulating the stability of surface AMPARs.

Both inflammatory processes and glutamatergic systems have been implicated in the pathophysiology of mood-related disorders. However, the role of caspase-1, a classic inflammatory caspase, in behavioral responses to chronic stress remains largely unknown. To address this issue, we examined the effects and underlying mechanisms of caspase-1 on preclinical murine models of depression. We found that loss of caspase-1 expression in Caspase-1-/- knockout mice alleviated chronic stress-induced depression-like behaviors, whereas overexpression of caspase-1 in the hippocampus of wild-type (WT) mice was sufficient to induce depression- and anxiety-like behaviors. Furthermore, chronic stress reduced glutamatergic neurotransmission and decreased surface expression of glutamate receptors in hippocampal pyramidal neurons of WT mice, but not Caspase-1-/- mice. Importantly, pharmacological inhibition of caspase-1-interleukin-1ß (IL-1ß) signaling pathway prevented the depression-like behaviors and the decrease in surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) in stressed WT mice. Finally, the effects of chronic stress on both depression- and anxiety-like behaviors can be mimicked by exogenous intracerebroventricular (i.c.v.) administration of IL-1ß in both WT and Caspase-1-/- mice. Taken together, our findings demonstrate that an increase in the caspase-1/IL-1ß axis facilitates AMPAR internalization in the hippocampus, which dysregulates glutamatergic synaptic transmission, eventually resulting in depression-like behaviors. These results may represent an endophenotype for chronic stress-induced depression.

The in vitro cytotoxicity of ascorbate depends on the culture medium used to perform the assay and involves hydrogen peroxide.

Reports about the effects of ascorbate (vitamin C) on cultured cells are confusing and conflicting. Some authors show inhibition of cell death by ascorbate, whereas others demonstrate that ascorbate is cytotoxic. In this report, using three different cell types and two different culture media (Dulbecco's modified Eagle's medium and RPMI 1640), we show that the toxicity of ascorbate is due to ascorbate-mediated production of H2O2, to an extent that varies with the medium used to culture the cells. For example, 1 mM ascorbate generates 161 +/- 39 microM H2O2 in Dulbecco's modified Eagle's medium and induces apoptosis in 50% of HL60 cells, whereas in RPMI 1640 only 83 +/- 17 microM H2O2 is produced and no apoptosis is detected. Apoptosis is prevented by catalase, and direct addition of H2O2 at the above concentration to the cells has similar effects to ascorbate. These results show that ascorbate itself is not toxic to the cell lines used and that effects of ascorbate in vivo cannot be predicted from studies on cultured cells. The ability of ascorbate to interact with different cell culture media to produce H2O2 at different rates could account for many or all of the conflicting results obtained using ascorbate in cultured cell assays.

Hydrogen peroxide in the human body.

Hydrogen peroxide (H(2)O(2)) is widely regarded as a cytotoxic agent whose levels must be minimized by the action of antioxidant defence enzymes. In fact, H(2)O(2) is poorly reactive in the absence of transition metal ions. Exposure of certain human tissues to H(2)O(2) may be greater than is commonly supposed: substantial amounts of H(2)O(2) can be present in beverages commonly drunk (especially instant coffee), in freshly voided human urine, and in exhaled air. Levels of H(2)O(2) in the human body may be controlled not only by catabolism but also by excretion, and H(2)O(2) could play a role in the regulation of renal function and as an antibacterial agent in the urine. Urinary H(2)O(2) levels are influenced by diet, but under certain conditions might be a valuable biomarker of 'oxidative stress'.

Artifacts in cell culture: rapid generation of hydrogen peroxide on addition of (-)-epigallocatechin, (-)-epigallocatechin gallate, (+)-catechin, and quercetin to commonly used cell culture media.

There is considerable current interest in the possible beneficial health effects of quercetin, catechins, epigallocatechins, epigallocatechin gallates, and related phenolic compounds found in teas, wines, and other plant products. As a result, many laboratories are studying the effects of these compounds on cells in culture. The present paper shows that addition of these compounds to commonly used cell culture media leads to generation of substantial amounts of hydrogen peroxide (H(2)O(2)). Dulbecco's modified Eagle medium gives the highest H(2)O(2) level for all the compounds tested, with levels reaching >400 microM within 2 h for addition of 1 mM concentrations of gallic acid, epigallocatechin gallate, and epigallocatechin. Catechin and quercetin produced lower, but still significant, levels of H(2)O(2). McCoy's 5A and RPMI 1640 media also promoted H(2)O(2) production from the above phenolic compounds. This rapid generation of H(2)O(2) could account for some or all of the reported effects of phenolic compounds on cells in culture.

Coffee drinking increases levels of urinary hydrogen peroxide detected in healthy human volunteers.

Freshly-voided human urine contains significant concentrations of hydrogen peroxide (H2O2). This H2O2 appears to arise in whole or in part by superoxide-dependent autoxidation of urinary biomolecules. Since instant coffee also contains high levels of H2O2, we examined the effect of coffee drinking on urinary levels of H2O2. Studies on healthy human volunteers showed that coffee drinking is rapidly and reproducibly followed by increased levels of H2O2 detectable in the urine for up to 2 h after drinking the coffee. The levels of H2O2 detected in urine suggest that exposure of human tissues to H2O2 may be greater than is commonly supposed. It is possible that H2O2 in urine could act as an antibacterial agent, and that H2O2 is involved in the regulation of glomerular function.

The antioxidant activities of seasonings used in Asian cooking. Powerful antioxidant activity of dark soy sauce revealed using the ABTS assay.

Scavenging of the ABTS (2,2'-azinobis[3-ethylbenzothiazoline-6-sulphonate])-derived nitrogen-centred radical cation (ABTS*+) was used to compare the total antioxidant activities of several seasonings used in Asian cooking. The results were expressed as Trolox equivalent antioxidant capacity (TEAC). The TEAC activities of dark soy sauces were found to be exceptionally high. In evaluating the TEAC of commercial products, attention must be paid to the addition of preservatives by manufacturers to the seasonings tested. Sodium benzoate (a preservative added to several seasonings) did not react significantly with ABTS*+, but the sulphite content of certain white wines may have led to an over-estimation of their TEAC.

Hydrogen peroxide. Ubiquitous in cell culture and in vivo?

Hydrogen peroxide (H2O2) is widely regarded as a cytotoxic agent whose levels must be minimized by the action of antioxidant defence enzymes. In fact, H2O2 is poorly reactive in the absence of transition metal ions. Exposure of certain human tissues to H2O2 may be greater than is commonly supposed; levels of H2O2 in the human body may be controlled not only by catabolism but also by excretion, and H2O2 could play a role in the regulation of renal function and as an antibacterial agent in the urine. Cell culture is a widely used method for the investigation of "physiological" processes such as signal transduction and regulation of gene expression, but chemical reactions involving cell culture media are rarely considered. Addition of reducing agents to commonly used cell-culture media can lead to generation of substantial amounts of H2O2. Some or all of the reported effects of ascorbic acid and polyphenolic compounds (e.g., quercetin, catechin, epigallocatechin, epigallocatechin gallate) on cells in culture may be due to H2O2 generation by interaction of these compounds with cell culture media.

Generation of hydrogen peroxide by "antioxidant" beverages and the effect of milk addition. Is cocoa the best beverage?

The ability of several beverages to generate hydrogen peroxide was demonstrated by direct measurement using the ferrous ion oxidation-xylenol orange (FOX) assay. Tea and coffee could generate H2O2 to achieve levels over 100 microM, but cocoa did not. Milk decreased net H2O2 production by beverages and showed some ability to remove H2O2 itself, apparently not because of catalase activity. Hence several of the beverages commonly drunk by humans show a complex mixture of anti- and pro-oxidant abilities.

Hydrogen peroxide in human urine: implications for antioxidant defense and redox regulation.

The presence of hydrogen peroxide, at levels sometimes exceeding 100 microM, in human urine samples was established by three different assay methods: 2-oxoglutarate decarboxylation and the ferrous oxidation-xylenol orange (FOX) assay and an oxygen electrode. Detected levels of H(2)O(2) were decreased by addition of superoxide dismutase. We conclude that urine contains autooxidizable molecules that, upon exposure to 21% O(2), undergo rapid superoxide-dependent autooxidation reactions to generate H(2)O(2). The exposure of human tissues to hydrogen peroxide may be greater than is commonly supposed, which has implications in relation to the proposed role of this species in cell signaling.

Trends in return migration to the South.

The rate of return migration to the South rose by nearly 19 percent between the late 1950's and the late 1960's and was an important factor in changing the South's overall migration pattern. But an increase in the rate of return migration was somewhat less important in changing Southern migration than (1) a decline in the rate of out-migration of native Southerners and (2) an increase in the rate at which non-Southern-born persons move to the South. The probability of former migrants returning to the South was over four times greater for whites than for blacks in the 1955-1960 period and three and one-fourth times greater in the 1965-1970 period. Since 1970 the rate of return migration has apparently continued to rise at a faster rate for blacks, but the black rate of return migration is still below the white rate.