Taurine mitigates nitrite-induced methemoglobin formation and oxidative damage in human erythrocytes

How β-Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/emission of noxious intermediates. In this study, β-cyclodextrin-functionalized biochar (BC@β-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@β-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@β-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@β-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@β-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@β-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@β-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for β-CD in wastewater bioremediation.

Hyperglycemia enhances the generation of ROS and RNS that impair antioxidant power and cause oxidative damage in human erythrocytes

Hyperglycemia is a state in which excess glucose circulates in blood. Erythrocytes are in direct contact with this high glucose concentration and are greatly affected by it. We have examined the effect of hyperglycemic condition on isolated human erythrocytes under in vitro conditions. Erythrocytes were incubated with different concentrations of glucose (5, 15, 30, 45 mmol/L) for 24 h, and several biochemical parameters were determined. Treatment with high glucose concentrations increased heme degradation and methemoglobin level, while methemoglobin reductase activity was decreased. A significant increase in protein oxidation and lipid hydroperoxides with a decrease in total sulfhydryl content was seen. This suggested the generation of oxidative stress, which was confirmed by an enhanced production of reactive oxygen and nitrogen species. Hyperglycemia led to a significant decline in the antioxidant power of erythrocytes, lowering their ability to quench free radicals and reduce metal ions to lower oxidation states. The plasma membrane redox system was upregulated, while ascorbate free radical reductase activity was lowered. Glucose exposure inhibited the enzymes of glycolysis and hexose monophosphate shunt. Electron microscopy showed morphological changes resulting in the formation of echinocytes. Thus, the hyperglycemic condition generates reactive species that oxidize proteins, hemoglobin, and lipids; impair the total antioxidant capacity; and alter morphology in human erythrocytes.

Enhancement of dissimilatory nitrate/nitrite reduction to ammonium of Escherichia coli sp. SZQ1 by ascorbic acid: Mechanism and performance

Dissimilatory nitrate reduction to ammonium (DNRA) can be used for nitrogen recovery. However, due to the low conversion efficiency of the DNRA process of microorganisms, the process cannot be industrially applied. Ascorbic acid (ASA) can improve DNRA efficiency of Escherichia coli sp. SZQ1 (E. coli). Experimental studies suggest that 10 g L^-1 ASA promoted DNRA process of E. coli at high concentrations of nitrite (10-20 mM). In the 5 g L^-1 ASA system, 9.2 mM nitrite was reduced to 8.21 mM ammonium by E. coli in 120 h. Mechanistic studies reveal that ASA reduced the oxidation-reduction potential (ORP) of the system and scavenged reactive oxygen species (ROS) in the cell of E. coli. Meanwhile, ASA was utilized by E. coli as the sole carbon source and provided electrons to DNRA process through ASA metabolic pathways. This study proposes a new strategy for increasing the efficiency of DNRA.

Short- and long-term effects of decabromodiphenyl ether (BDE-209) on sediment denitrification using a semi-continuous microcosm

The widespread use of decabromodiphenyl ether (BDE-209) resulted in its deposition in environmental media and biological matrices. However, to date, few studies focused on the effect of BDE-209 on microorganisms, and those available were investigated via an enclosed system completely cutting off the communication between testing system and its native environment. Herein, 4.0 mg/g BDE-209 acute exposure induced a 20% decline of NO_X-N (the sum of NO₃^--N and NO₂^--N) removal efficiency and a significant accumulation of NO₂^--N and N₂O. These inhibitory effects presented in a BDE-209 concentration-dependent manner. Using a semi-continuous microcosm, the inhibitory effects of BDE-209 on denitrification were observed to be significantly enhanced with the extending of exposure duration. Denitrifying genes assay illustrated that BDE-209 has an insignificant effect on the global abundance of denitrifying bacteria because of microbial exchange with its overlying water. But the utilization of electron donor (carbon substrate), the activity of electron transport system and denitrifying enzymes were significantly inhibited by BDE-209 exposure in a exposure-duration-dependent manner. Finally, insufficient electron donor and lower efficiency of electron transport and utilization on denitrifying enzymes deteriorated the denitrification performance. These results provided a new insight into BDE-209 influence on denitrification in the natural environment.

Ionic copper strengthens the toxicity of tetrabromobisphenol A (TBBPA) to denitrification by decreasing substrate transport and electron transfer

Increasing electrical and electronic waste have raised concerns about the potential toxicity of brominated flame retardants (BFRs) and heavy metals (HMs). However, few studies have focused on the combined effect of BFRs and HMs on microorganisms, especially denitrifying bacteria, which have an essential role in N cycles and N₂O emission. Herein, we investigate the combined effect of tetrabromobisphenol A (TBBPA) and Cu on model denitrifying bacteria. A further 24.5% decline in N removal efficiency was observed when 0.05 mg/L Cu were added into a denitrifying system containing 0.75 mg/L TBBPA. Further study demonstrated that Cu heightened the toxicity of TBBPA to denitrification via following aspects: (1) Cu stimulated EPS secretion induced by TBBPA during denitrification, blocked the transmembrane transport of glucose, which caused insufficient carbon substrate for bacteria growth and electron provision; (2) Cu further suppressed key denitrifying enzymes' activity and down-regulated genes involving electron transport induced by TBBPA, led to the decrease of electron transport activity. Finally, the decrease of bacterial growth, insufficient electron donor, and lower electron transport activity caused the synergetic toxic effect of TBBPA and Cu on denitrification. Overall, the present study provides new insights into the combined effect of BFRs and HMs on microorganisms.

Impact of taurine on red blood cell metabolism and implications for blood storage

BACKGROUND

Taurine is an antioxidant that is abundant in some common energy drinks. Here we hypothesized that the antioxidant activity of taurine in red blood cells (RBCs) could be leveraged to counteract storage-induced oxidant stress.

STUDY DESIGN AND METHODS

Metabolomics analyses were performed on plasma and RBCs from healthy volunteers (n = 4) at baseline and after consumption of a whole can of a common, taurine-rich (1000 mg/serving) energy drink. Reductionistic studies were also performed by incubating human RBCs with taurine ex vivo (unlabeled or ¹³ C¹⁵ N-labeled) at increasing doses (0, 100, 500, and 1000 μmol/L) at 37°C for up to 16 hours, with and without oxidant stress challenge with hydrogen peroxide (0.1% or 0.5%). Finally, we stored human and murine RBCs under blood bank conditions in additives supplemented with 500 μmol/L taurine, before metabolomics and posttransfusion recovery studies.

RESULTS

Consumption of energy drinks increased plasma and RBC levels of taurine, which was paralleled by increases in glycolysis and glutathione (GSH) metabolism in the RBC. These observations were recapitulated ex vivo after incubation with taurine and hydrogen peroxide. Taurine levels in the RBCs from the REDS-III RBC-Omics donor biobank were directly proportional to the total levels of GSH and glutathionylated metabolites and inversely correlated to oxidative hemolysis measurements. Storage of human RBCs in the presence of taurine improved energy and redox markers of storage quality and increased posttransfusion recoveries in FVB mice.

CONCLUSION

Taurine modulates RBC antioxidant metabolism in vivo and ex vivo, an observation of potential relevance to transfusion medicine.

Tetrabromobisphenol A (TBBPA) inhibits denitrification via regulating carbon metabolism to decrease electron donation and bacterial population

The potential risks of brominated flame retardants (BFRs) like tetrabromobisphenol A (TBBPA) have attracted much attention. However, the influence of TBBPA on functional microbes remains poorly understood, especially with regards to denitrification, which is closely related with the carbon and nitrogen cycles, eutrophication and greenhouse gas emission. Herein, we found that 1.0 mg/L of TBBPA significantly decreased the total nitrogen removal efficiency by 81.7%, but increased the accumulation of NO₂^--N (by 81.5%) and N₂O (by 172-fold). This was found to be underlie by the significant decrease in both the denitrifying capability of denitrifiers and total bacterial population. Further investigation revealed that TBBPA inhibited the pathways of glucolysis and pentose phosphate, and promoted glyoxylate bypass via regulating genes expressions of key enzymes (such as glucose-6-phosphate isomerase, pyruvate dehydrogenase, isocitrate lyase, etc.), then decreased the generation of NADH serving as electron donor for denitrification, and inhibited the denitrifying capability of denitrifiers. Moreover, insufficient NADH stimulated the accumulation of denitrifying intermediates (NO₂^--N and N₂O), which induced the increase of reactive nitrogen species (RNS), whose accumulation decreased proliferation and increased apoptosis of denitrifying bacteria. Finally, the decrease in the denitrifying capability of denitrifier and bacterial population resulted in negative denitrifying performance.