Application of biochar and humic acid improves the physiological and biochemical processes of rice (Oryza sativa L.) in conferring plant tolerance to arsenic-induced oxidative stress.

Biochar (BC) and humic acid (HA) are well-documented in metal/metalloid detoxification, but their regulatory role in conferring plant oxidative stress under arsenic (As) stress is poorly understood. Therefore, we aimed at investigating the role of BC and HA (0.2 and 0.4 g kg-1 soil) in the detoxification of As (0.25 mM sodium arsenate) toxicity in rice (Oryza sativa L. cv. BRRI dhan75). Arsenic exhibited an increased lipid peroxidation, hydrogen peroxide, electrolyte leakage, and proline content which were 32, 30, 9, and 89% higher compared to control. In addition, the antioxidant defense system of rice consisting of non-enzyme antioxidants (18 and 43% decrease in ascorbate and glutathione content) and enzyme activities (23-50% reduction over control) was decreased as a result of As toxicity. The damaging effect of As was prominent in plant height, biomass acquisition, tiller number, and relative water content. Furthermore, chlorophyll and leaf area also exhibited a decreasing trend due to toxicity. Arsenic exposure also disrupted the glyoxalase system (23 and 33% decrease in glyoxalase I and glyoxalase II activities). However, the application of BC and HA recovered the reactive oxygen species-induced damages in plants, upregulated the effectiveness of the ascorbate-glutathione pool, and accelerated the activities of antioxidant defense and glyoxalase enzymes. These positive roles of BC and HA ultimately resulted in improved plant characteristics with better plant-water status and regulated proline content that conferred As stress tolerance in rice. So, it can be concluded that BC and HA effectively mitigated As-induced physiology and oxidative damage in rice plants. Therefore, BC and HA could be used as potential soil amendments in As-contaminated rice fields.

Neural Glyoxalase Pathway Enhancement by Morin Derivatives in an Alzheimer's Disease Model.

The glyoxalase pathway (GP) is an antioxidant defense system that detoxifies metabolic byproduct methylglyoxal (MG). Through sequential reactions, reduced glutathione (GSH), glyoxalase I (glo-1), and glyoxalase II (glo-2) convert MG into d-lactate. Spontaneous reactions involving MG alter the structure and function of cellular macromolecules through the formation of inflammatory advanced glycation endproducts (AGEs). Accumulation of MG and AGEs in neural cells contributes to oxidative stress (OS), a state of elevated inflammation commonly found in neurodegenerative diseases including Alzheimer's disease (AD). Morin is a common plant-produced flavonoid polyphenol that exhibits the ability to enhance the GP-mediated detoxification of MG. We hypothesize that structural modifications to morin will improve its inherent GP enhancing ability. Here we synthesized a morin derivative, dibromo-morin (DBM), formulated a morin encapsulated nanoparticle (MNP), and examined their efficacy in enhancing neural GP activity. Cultured mouse primary cerebellar neurons and Caenorhabditis elegans were induced to a state of OS with MG and treated with morin, DBM, and MNP. Results indicated the morin derivatives were more effective compared to the parent compound in neural GP enhancement and preventing MG-mediated OS in an AD model.

Inhibition of proliferation of human promyelocytic leukaemia HL60 cells by S-D-lactoylglutathione in vitro.

Human promyelocytic leukaemia HL60 cells were incubated with the glyoxalase intermediate S-D-lactoylglutathione in culture. The effects on cell proliferation, maturation, viability and cell cycle were investigated. When HL60 cells (5 x 10(4)/ml) were incubated with 50-500 microM S-D-lactoylglutathione for two days, the rate of cell proliferation was decreased. This effect was maximal at 500 microM S-D-lactoylglutathione where the cell proliferation rate was only 16% of control levels. There was a concomitant decrease in cell viability but little differentiation. During the first day of treatment, there was a significant decrease in the percentage of cells in the G2-M phase of the cell cycle with a concomitant increase in the G0-G1 phase. In contrast, when HL60 cells were incubated with 1.0-1.5 mM S-D-lactoylglutathione, the inhibition of cell proliferation was progressively lifted, with a concomitant increase in the percentage of differentiated cells (27% differentiation with 1.5 mM S-D-lactoylglutathione). The activities of glyoxalase II and gamma-glutamyl transpeptidase were increased in these cells. S-D-Lactoylglutathione slowly entered the HL60 cells and was consumed over the period when changes in cell cycle distribution, growth arrest and decrease in cell viability were observed. The mechanism of inhibition of proliferation of HL60 promyelocytes by S-D-lactoylglutathione is unknown but it may be related to the ability of S-D-lactoylglutathione to stimulate the assembly of microtubules.

The effect of glyoxalase I on the metabolism of 4,5-dioxovaleric acid.

Biosynthesis of 5-aminolevulinic acid in mammalian cells is catalyzed by aminolevulinic acid synthase in a condensation reaction utilizing glycine and succinyl X coenzyme A. An alternate pathway in mammalian cells may involve the biosynthesis of aminolevulinic acid via a transamination reaction in which L-alanine is the amino donor and 4,5-dioxovaleric acid is the acceptor. This transamination reaction, or one very similar, is employed by plants for the biosynthesis of aminolevulinic acid which is ultimately converted to chlorophyll. The effect of glyoxalase I on the diversion of dioxovaleric acid to other products was tested using both purified glyoxalase I and crude tissue homogenates. Glyoxalase I is a metalloenzyme and glutathione is a co-substrate. Purified glyoxalase I reduced the amount of aminolevulinic acid formed in the presence of dioxovaleric acid, L-alanine, glutathione, and purified L-alanine: 4,5-dioxovaleric acid aminotransferase (dioxovalerate transaminase). The conversion of dioxovaleric acid to aminolevulinic acid was inhibited by the addition of glutathione when a dialyzed bovine liver homogenate served as the source of both glyoxalase I and dioxovalerate transaminase. Removal of metals from bovine liver homogenates produced an 85% decrease in glyoxalase I activity. These 'metal-free' homogenates still affected the conversion of dioxovaleric acid to aminolevulinic acid after preincubation with MgSO4. The effect of glyoxalase I on the metabolism of dioxovaleric acid was also studied using a fluorometric enzyme assay for the quantification of dioxovaleric acid via a coupled enzyme reaction converting it to uroporphyrin. Homogenates of both liver and barley diminished the amount of dioxovaleric acid detected by the coupled assay, but this effect could be prevented by dialysis of the homogenates. Addition of glutathione to dialyzed homogenates markedly reduced the amount of uroporphyrin generated from dioxovaleric acid. Metal-free homogenates supplemented with glutathione reduced the conversion of dioxovaleric acid to uroporphyrin in the coupled assay, but preincubation with MgSO4 greatly augmented this effect. These studies point out the difficulty in evaluating dioxovaleric acid as a heme precursor using whole cell homogenates.

Inhibition of protein and DNA synthesis in tissue culture cells by a derivative of methyl glyoxal and ascorbate.

The inhibitory effect of a methyl glyoxal-ascorbate (MGA) adduct (NFCR 278021) on protein and DNA synthesis in monolayer cultures of GPK epithelial cells has been compared with the inhibitory action of methyl glyoxal (MG). GPK cells exhibited an ID50 of 0.98 microM MG for both protein and DNA synthesis compared with an ID50 of 0.92 mM for the adduct. Hill plots demonstrate that the characteristics of the receptor saturation are the same for MG and MGA, suggesting that the action of the two agents is mediated through the MG moiety which is modified by the presence of the ascorbate portion of the molecule in MGA. It is shown that MGA undergoes spontaneous oxidation in solution and is a substrate for ascorbate oxidase, but that no additional MG activity is released by total enzymic oxidation of MGA, and oxidised MGA possesses the same inhibitory characteristics as MGA. Inhibition of protein synthesis by ascorbate or dehydroascorbate were not demonstrated in the dose range employed for MGA. The inhibitory effect of the adduct on protein synthesis was found to be diminished in the presence of glutathione and glyoxalase I (Glo I) and II( Glo II).