Nitrite accumulation in comammox-dominated nitrification-denitrification reactors: Effects of DO concentration and hydroxylamine addition.

In this study, nitrite accumulation was investigated under different DO conditions and different hydroxylamine addition methods during the domestic wastewater treatment. Two sequencing batch reactors in parallel were operated under cyclic aerobic and anoxic conditions with the DO concentration of 2.0 and 4.0 mg/L in aerobic phase. The nitrite accumulation rate during high DO conditions increased to 44.8 and 66.7% in 20 days. During hydroxylamine addition, the NAR increased over 90% under the continuous and intermittent hydroxylamine addition. Continuous hydroxylamine addition could result in a more efficient and rapid nitrite accumulation. The findings suggested that comammox could be the main reason for the failure of partial nitrification in a low DO environment (< 0.5 mg/L). The nitrogen variation during typical cycles showed that the continuous hydroxylamine addition suppressed the activity of NOB and the ammonia oxidation rate. Further, the qPCR results indicated that the abundance of comammox amoA (ranged from 6.25 × 107 to 4.16 × 108 copies/g VSS) was higher than those of AOB amoA and Nitrobacter in sludge samples. The findings from the current study may enrich our understanding of partial nitrification and its control strategy.

An Intratumor Pharmacokinetic/Pharmacodynamic Model for the Hypoxia-Activated Prodrug Evofosfamide (TH-302): Monotherapy Activity is Not Dependent on a Bystander Effect.

Tumor hypoxia contributes to resistance to anticancer therapies. Hypoxia-activated prodrugs (HAPs) selectively target hypoxic cells and their activity can extend to well-oxygenated areas of tumors via diffusion of active metabolites. This type of bystander effect has been suggested to be responsible for the single agent activity of the clinical-stage HAP evofosfamide (TH-302) but direct evidence is lacking. To dissect the contribution of bystander effects to TH-302 activity, we implemented a Green's function pharmacokinetic (PK) model to simulate the spatial distribution of O2, TH-302 and its cytotoxic metabolites, bromo-isophosphoramide mustard (Br-IPM) and its dichloro derivative isophosphoramide mustard (IPM), in two digitized tumor microvascular networks. The model was parameterized from literature and experimentally, including measurement of diffusion coefficients of TH-302 and its metabolites in multicellular layer cultures. The latter studies demonstrate that Br-IPM and IPM cannot diffuse significantly from the cells in which they are generated, although evidence was obtained for diffusion of the hydroxylamine metabolite of TH-302. The spatially resolved PK model was linked to a pharmacodynamic (PD) model that describes cell killing probability at each point in the tumor microregion as a function of Br-IPM and IPM exposure. The resulting PK/PD model accurately predicted previously reported monotherapy activity of TH-302 in H460 tumors, without invoking a bystander effect, demonstrating that the notable single agent activity of TH-302 in tumors can be accounted for by significant bioreductive activation of TH-302 even in oxic regions, driven by the high plasma concentrations achievable with this well-tolerated prodrug.

Effects of H2S on the central regulation of respiration in adult rats.

Hydrogen sulfide (H2S) is a gasotransmitter synthesized from cysteine (Cys) by pyridoxal-5'-phosphate-dependent enzymes. We investigated the potential roles of H2S in the regulation of central rhythmic respiration in adult rats in vivo. Sodium hydrosulfide (NaHS: 2.5 mM, 10 mM, and 5 mM) as a source of exogenous H2S, Cys (2.5 mM, 10 mM and 5 mM) as a source of endogenous H2S, 2.5 mM Cys+10 mM hydroxylamine (NH2OH), and 10 mM NH2OH, respectively, were intracerebroventricularly injected into rats. The rhythmic discharge of the diaphragm, including burst duration (BD), burst interval (BI), burst frequency (BF), and integrated amplitude (IA), and arterial blood pressure (BP) were measured at different time points. The results were analyzed by analysis of variance. A total of 2.5 mM NaHS did not significantly affect changes in BD, BI, BF, IA, or BP (P>0.05), whereas 2.5 mM Cys significantly altered BD, BI, and BF (P<0.05); however, there was no change in IA and BP (P>0.05). A concentration of 5 mM Cys had effects similar to those of 5 mM NaHS; both induced biphasic respiratory responses and changed the BF (P<0.05). A concentration of 10 mM NH2OH irreversibly inhibited rhythmic discharge of the diaphragm except for IA. No change was seen in BI, BF, IA, or BP (P>0.05) except for BD was temporarily decreased (P<0.05) in the 2.5 mM Cys+10 mM NH2OH group. These results suggest that exogenous and endogenous H2S may participate in the regulation of respiratory activity in adult rats.

Redox evaluation in sepsis model mice by the in vivo ESR technique using acyl-protected hydroxylamine.

In vivo electron spin resonance (ESR) spectroscopy is a noninvasive technique that measures the oxidative stress in living experimental animals. The rate of decay of the ESR signal right after an injection of nitroxyl radical has been measured to evaluate the oxidative stress in animals, although the probe's disposition could also affect this rate. Because the amount of probes forming the redox pair of hydroxyl amine and its corresponding nitroxyl radical was shown to be nearly constant in most organs or tissues 10min after the injection of 1-acetoxy-3-carbamoyl-2,2,5,5-tetramethylpyrrolidine (ACP) in mice, we evaluated the oxidative stress in sepsis model mice induced by lipopolysaccharide (LPS) by intravenously injecting ACP as a precursor of redox probes. The in vivo ESR signal increased up to 7-8min after the ACP injection and then decreased. Decay of the in vivo signal in LPS-treated mice was significantly slower than that in healthy mice, whereas no significant difference was observed in the rate of change in the total amount of redox probes in the blood and liver between these groups. ESR imaging showed that the in vivo signals observed at the chest and upper abdomen decayed slowly in LPS-treated mice. Suppression of the decay in LPS-treated mice was canceled by the administration of a combination of pegylated superoxide dismutase and catalase, or an inhibitor of nitric oxide synthase, or gadolinium chloride. These results indicate that the LPS-treated mouse is under oxidative stress and that reactive oxygen species, such as superoxide and peroxynitrite, related to macrophages are mainly involved in the oxidative stress.

Protection by an oral disubstituted hydroxylamine derivative against loss of retinal ganglion cell differentiation following optic nerve crush.

Thy-1 is a cell surface protein that is expressed during the differentiation of retinal ganglion cells (RGCs). Optic nerve injury induces progressive loss in the number of RGCs expressing Thy-1. The rate of this loss is fastest during the first week after optic nerve injury and slower in subsequent weeks. This study was undertaken to determine whether oral treatment with a water-soluble N-hydroxy-2,2,6,6-tetramethylpiperidine derivative (OT-440) protects against loss of Thy-1 promoter activation following optic nerve crush and whether this effect targets the earlier quick phase or the later slow phase. The retina of mice expressing cyan fluorescent protein under control of the Thy-1 promoter (Thy1-CFP mice) was imaged using a blue-light confocal scanning laser ophthalmoscope (bCSLO). These mice then received oral OT-440 prepared in cream cheese or dissolved in water, or plain vehicle, for two weeks and were imaged again prior to unilateral optic nerve crush. Treatments and weekly imaging continued for four more weeks. Fluorescent neurons were counted in the same defined retinal areas imaged at each time point in a masked fashion. When the counts at each time point were directly compared, the numbers of fluorescent cells at each time point were greater in the animals that received OT-440 in cream cheese by 8%, 27%, 52% and 60% than in corresponding control animals at 1, 2, 3 and 4 weeks after optic nerve crush. Similar results were obtained when the vehicle was water. Rate analysis indicated the protective effect of OT-440 was greatest during the first two weeks and was maintained in the second two weeks after crush for both the cream cheese vehicle study and water vehicle study. Because most of the fluorescent cells detected by bCSLO are RGCs, these findings suggest that oral OT-440 can either protect against or delay early degenerative responses occurring in RGCs following optic nerve injury.

In vitro and ex vivo activity of peptide deformylase inhibitors against Mycobacterium tuberculosis H37Rv.

Bacterial peptide deformylase (PDF) catalyses removal of the N-terminal formyl group of proteins and is essential for protein maturation, growth and survival of bacteria. Thus, PDF appears to be a good antimycobacterial drug target. In the present study, various well-known PDF inhibitors, such as BB-3497, actinonin, 1,10-phenanthroline, hydroxylamine hydrochloride and galardin, were selected to evaluate their inhibitory activity against Mycobacterium tuberculosis. All compounds were found to be active against M. tuberculosis, with MIC(90) values (lowest drug concentration at which 90% of growth was inhibited on the basis of CFU enumeration) ranging from 0.2 mg/L to 74 mg/L. BB-3497 and 1,10-phenanthroline exhibited potent in vitro antimycobacterial activity, and also showed synergism with isoniazid and rifampicin. All compounds showed a bacteriostatic mode of inhibition. Under ex vivo conditions and short-course chemotherapy, BB-3497 and actinonin were found to be significantly active, with BB-3497 exhibiting comparable efficacy to that of isoniazid. Collectively, promising activities of PDF inhibitors such as BB-3497 and actinonin suggest their potential use against M. tuberculosis.

Protective effect of TEMPOL derivatives against light-induced retinal damage in rats.

PURPOSE: OT-551 (1-hydroxy-4-cyclopropanecarbonyloxy-2,2,6,6-tetramethylpiperidine hydrochloride), a TEMPOL-H (OT-674) derivative, is a new catalytic antioxidant. In the present study, the efficacy of OT-551 and OT-674 in retinal neuroprotection was tested in a model of light-induced photoreceptor degeneration. METHODS: Albino rats were intraperitoneally injected with OT-551, OT-674, or water, approximately 30 minutes before a 6-hour exposure to 2700-lux white fluorescent light. Retinal protection was evaluated histologically by measuring the thickness of the outer nuclear layer (ONL) and functionally by electroretinogram (ERG) analysis, 5 to 7 days after exposure to light. Levels of protein modification by 4-hydroxynonenal (4-HNE) and 4-hydroxyhexenal (4-HHE), which are end products of the nonenzymatic oxidation of n-6 and n-3 polyunsaturated fatty acids, respectively, were measured by Western dot blot analysis immediately after exposure to light. RESULTS: After exposure to light, water-treated animals had a 77% loss of ERG b-wave amplitudes and a 26% and 56% loss of mean ONL thickness in the inferior and superior hemispheres, respectively. Compared with water-treated rats, ERG b-wave amplitudes in light-exposed eyes were significantly higher in 25 (P < 0.05)-, 50 (P < 0.05)-, and 100 (P < 0.001)-mg/kg OT-551-treated rats. Mean ONL thickness in the superior hemisphere was significantly higher in 25 (P < 0.01)-, 50 (P < 0.01)-, and 100 (P < 0.001)-mg/kg OT-551-treated, light-exposed eyes and in 100 mg/kg (P < 0.05) OT-674-treated eyes. No decrease of ONL thickness was observed in the light-protected covered fellow eyes in any animal. Increased levels of 4-HNE- and 4-HHE-protein modifications after exposure to light in water-treated eyes were completely counteracted by 100 mg/kg OT-551. CONCLUSIONS: Systemic administration of OT-551 and OT-674 provides both functional and morphologic photoreceptor cell protection against acute light-induced damage, most likely by inhibiting lipid peroxidation. The protection by OT-551 was greater than OT-674.