Effect of release of dopamine on iron transformations and reactive oxygen species (ROS) generation under conditions typical of coastal waters

Seed-Borne Erwinia persicina Affects the Growth and Physiology of Alfalfa (Medicago sativa L.)

Seed-borne Erwinia persicina can be transmitted globally via alfalfa (Medicago sativa L.) seed trade, but there is limited information about the impact of this plant-pathogenic bacterium on alfalfa plants. In this study, strain Cp2, isolated from alfalfa seeds, was confirmed by whole-genome sequencing to belong to E. persicina. Subsequently, the effects of Cp2 on alfalfa growth and physiology were evaluated by constructing a rhizosphere infection model. Strain Cp2 had a strong inhibitory effect on the elongation and growth of alfalfa roots, which was very unfavorable to these perennial plants. Furthermore, an increased number of leaf spots and yellowing symptoms were observed in plants of the Cp2 group from day 10 to day 21 and the strain Cp2 was re-isolated from these leaves. Correlation between growth and photosynthetic parameters was analyzed and the significant decreases in fresh weight and root and plant lengths in the Cp2 group were related to the marked reduction of chlorophyll b, carotenoid, transpiration rate, and stomatal conductance of leaves (r > 0.75). In addition, nine physiological indicators of root, stem, and leaf were measured in the plants 21 days after treatment with Cp2. The physiological response of root and leaf to Cp2 treatment was stronger than that of stem. The physiological indicators with the greatest response to Cp2 infection were further explored through principal component analysis, and superoxide dismutase, peroxidase, ascorbate peroxidase, and soluble protein showed the greatest changes in roots, stems, and leaves (P < 0.001). Among tissues, the commonality was the change of soluble protein. Therefore, soluble protein is speculated to be a physiological marker during alfalfa–E. persicina interactions. These findings indicate that once E. persicina spreads from alfalfa seeds to the rhizosphere, it can invade alfalfa roots and cause disease. This study demonstrates that this plant pathogenic bacterium may be a potential threat to new environment when they spread via seed trade and these “dangerous hitchhikers” warrant further attention, especially in the study of bacterial diseases in pasture-based production systems.

Fe(II) Redox Chemistry in the Environment

Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.

Effectiveness of the Iron Chelator CN128 in Mitigating the Formation of Dopamine Oxidation Products Associated with the Progression of Parkinson's Disease

The occurrence and progression of Parkinson's disease (PD) has been associated with the observation of elevated iron concentrations in the substantia nigra pars compacta (SNpc). While the reasons for the impact of elevated iron concentrations remain unclear, one hypothesis is that the presence of labile iron induces the oxidation of dopamine (DA) to toxic quinones such as aminochrome (DAC) and reactive oxygen species (ROS). As such, one of the proposed therapeutic strategies has been the use of iron chelators such as deferiprone (DFP) (which is recognized to have limitations related to its rapid degradation in the liver) to reduce the concentration of labile iron. In this study, a detailed investigation regarding the novel iron chelator, CN128, was conducted and a kinetic model developed to elucidate the fundamental behavior of this chelator. The results in this work reveal that CN128 is effective in alleviating the toxicity induced by iron and DA to neurons when DA is present at moderate concentrations. When all the iron is chelated by CN128, the formation of DAC and the oxidation of DA can be reduced to levels identical to that in the absence of iron. The production of H₂O₂ is lower than that generated via the autoxidation of the same amount of DA. However, when severe leakage of DA occurs, the application of CN128 is insufficient to alleviate the associated toxicity. This is attibuted to the less important role of iron in the production of toxic intermediates at high concentrations of DA. CN128 is superior to DFP with regard to the reduction in formation of DAC and elevation in DA concentration. In summary, the results of this study suggest that prodromal application of the chelator CN128 could be effective in preventing the onset and slowing the early stage development of PD symptoms associated with oxidants and toxic intermediates resulting from the iron-mediated oxidation of the neurotransmitter dopamine with CN128 likely to be superior to DFP in view of its greater in vivo availability and less problematic side effects.

Enzymatic and non-enzymatic pathways of kynurenines' dimerization: the molecular factors for oxidative stress development

Kynurenines, the products of tryptophan oxidative degradation, are involved in multiple neuropathologies, such as Huntington's chorea, Parkinson's disease, senile dementia, etc. The major cause for hydroxykynurenines's neurotoxicity is the oxidative stress induced by the reactive oxygen species (ROS), the by-products of L-3-hydroxykynurenine (L-3HOK) and 3-hydroxyanthranilic acid (3HAA) oxidative self-dimerization. 2-aminophenol (2AP), a structural precursor of L-3HOK and 3HAA, undergoes the oxidative conjugation to form 2-aminophenoxazinone. There are several modes of 2AP dimerization, including both enzymatic and non-enzymatic stages. In this study, the free energies for 2AP, L-3HOK and 3HAA dimerization stages have been calculated at B3LYP/6-311G(d,p)//6-311+(O)+G(d) level, both in the gas phase and in heptane or water solution. For the intermediates, ionization potentials and electron affinities were calculated, as well as free energy and kinetics of molecular oxygen interaction with several non-enzymatically formed dimers. H-atom donating power of the intermediates increases upon the progress of the oxidation, making possible generation of hydroperoxyl radical or hydrogen peroxide from O2 at the last stages. Among the dimerization intermediates, 2-aminophenoxazinole derivatives have the lowest ionization potential and can reduce O2 to superoxide anion. The rate for O-H homolytic bond dissociation is significantly higher than that for C-H bond in non-enzymatic quinoneimine conjugate. However, the last reaction passes irreversibly, reducing O2 to hydroperoxyl radical. The inorganic ferrous iron and the heme group of Drosophila phenoxazinone synthase significantly reduce the energy cost of 2AP H-atom abstraction by O2. We have also shown experimentally that total antioxidant capacity decreases in Drosophila mutant cardinal with L-3HOK excess relative to the wild type Canton-S, and lipid peroxidation decreases in aged cardinal. Taken together, our data supports the conception of hydroxykynurenines' dual role in neurotoxicity: serving as antioxidants themselves, blocking lipid peroxidation by H-atom donation, they also can easily generate ROS upon dimerization, leading to the oxidative stress development.

Kinetic Modeling of pH-Dependent Oxidation of Dopamine by Iron and Its Relevance to Parkinson's Disease

Parkinson's disease is the second most common neurodegenerative disease. While age is the most significant risk factor, the exact cause of this disease and the most effective approaches to mitigation remain unclear. It has long been proposed that dopamine may play a role in the pathology of Parkinson's disease in view of its ability to generate both protein-modifying quinones such as aminochrome and reactive oxygen species, especially in the presence of pathological iron accumulation in the primary site of neuron loss. Given the clinically measured acidosis of post-mortem Parkinson's disease brain tissue, the interaction between dopamine and iron was investigated over a pH range of 7.4 to 6.5 with emphasis on the accumulation of toxic quinones and generation of reactive oxygen species. Our results show that the presence of iron accelerates the formation of aminochrome with ferrous iron (Fe[II]) being more efficient in this regard than ferric iron (Fe[III]). Our results further suggest that a reduced aminochrome rearrangement rate coupled with an enhanced turnover rate of Fe[II] as a result of brain tissue acidosis could result in aminochrome accumulation within cells. Additionally, under these conditions, the enhanced redox cycling of iron in the presence of dopamine aggravates oxidative stress as a result of the production of damaging reactive species, including hydroxyl radicals.

Mechanism Underlying the Effectiveness of Deferiprone in Alleviating Parkinson's Disease Symptoms

Elevation in iron content as well as severe depletion of dopamine (DA) as a result of iron-induced loss of dopaminergic neurons has been recognized to accompany the progression of Parkinson's disease (PD). To better understand the mechanism of the mitigating effect of the iron chelator deferiprone (DFP) on PD, the interplay between iron and DFP was investigated both in the absence and presence of DA. The results show that DFP was extremely efficient in scavenging both aqueous iron and iron that was loosely bound to DA with the entrapment of iron in Fe-DFP complexed form critical to halting the iron catalyzed degradation of DA and associated generation of toxic metabolites. The DFP related scavenging of dopamine semiquinone (DA^•-) and superoxide (O₂^•-) may also contribute to its positive effects in the treatment of PD.