Efficiency of methemoglobin, hemin and ferric citrate in catalyzing protein tyrosine nitration, protein oxidation and lipid peroxidation in a bovine serum albumin–liposome system: Influence of pH

(-)-Epigallocatechin gallate as an inhibitor of hemoglobin-catalyzed lipid oxidation: molecular mechanism of action and nutritional application

Hemoglobin (Hb) is effective inducer for lipid oxidation and protein-polyphenol interaction is a well-known phenomenon. The effects of the interaction of (-)-epigallocatechin gallate (EGCG) with Hb on lipid oxidation were rarely elucidated. The detailed interaction between bovine Hb and EGCG was systematically explored by experimental and theoretical approaches, to illustrate the molecular mechanisms by which EGCG influenced the redox states and stability of Hb. EGCG would bind to the central pocket of protein with one binding site to form Hb-EGCG complex. The binding constant for Hb-EGCG complex was 0.34 × 104 M-1 at 277 K, and thermodynamic parameters (ΔH > 0, ΔS > 0 and ΔG < 0) revealed the participation of hydrophobic forces in the binding process. The binding of EGCG would increase the compactness of protein molecule and diminish the crevice near the heme cavity, which was responsible for the reduction of met-Hb to oxy-Hb and inhibition of hemin release from met-Hb. Moreover, EGCG efficiently suppressed Hb-caused lipid oxidation in liposomes and cod muscles, which was possibly attributed to the reduction to oxy-Hb state and declined hemin dissociation from met-Hb. Altogether, our results provide significant insights into the binding of EGCG to redox-active Hb, which represents a novel mechanism for the anti-oxidant capacity of EGCG in human health and is favorable to the applications of natural EGCG in the good quality of Hb-containing products.

Binding of Quercetin to Hemoglobin Reduced Hemin Release and Lipid Oxidation

The interactions between quercetin and bovine (or human) hemoglobin (Hb) were systematically investigated by fluorescence, UV-vis absorption spectroscopy, and molecular docking to demonstrate the structural mechanism by which quercetin affected the Hb redox state and stability. Quercetin could interact with the central cavity of the Hb molecule with one binding site to generate an Hb-quercetin complex, and the hydrophobic interaction played an important role in the formation of the complex. The binding constant for the Hb-quercetin complex at 298 K was observed to be 1.25 × 10⁴ M^-1. In addition, quercetin effectively inhibited Hb-induced lipid oxidation in liposomes or washed muscles, which was ascribed to the conversion to oxy-Hb and decreased hemin dissociation from met-Hb. Consistent with its lower abilities to bind Hb and scavenge free radicals, rutin (i.e., quercetin-3-rhamnosylglucsoside) did not significantly influence the redox state of Hb nor reduce hemin release from Hb, and subsequently, it less effectively inhibited Hb-induced lipid oxidation than quercetin. Altogether, the results herein provide novel insights into the antioxidant mechanism for quercetin and are beneficial to the application of natural quercetin in Hb-containing foods.

Effects of lotus seedpod oligomeric procyanidins on the inhibition of AGEs formation and sensory quality of tough biscuits

The advanced glycation end products (AGEs) are formed in baked products through the Maillard reaction (MR), which are thought to be a contributing factor to chronic diseases such as heart diseases and diabetes. Lotus seedpod oligomeric procyanidins (LSOPC) are natural antioxidants that have been added to tough biscuit to create functional foods that may lower the risk of chronic diseases. The effect of LSOPC on AGEs formation and the sensory quality of tough biscuit were examined in this study. With the addition of LSOPC, the AGEs scavenging rate and antioxidant capacity of LSOPC-added tough biscuits were dramatically improved. The chromatic aberration (ΔE) value of tough biscuits containing LSOPC increased significantly. Higher addition of LSOPC, on the other hand, could effectively substantially reduced the moisture content, water activity, and pH of LSOPC toughen biscuits. These findings imply that using LSOPC as additive not only lowers the generation of AGEs, but also improves sensory quality of tough biscuit.

Free iron rather than heme iron mainly induces oxidation of lipids and proteins in meat cooking

In this study, the relationship between different forms of iron (free or binding) and oxidation of lipids, proteins in meat system were investigated. Pork tenderloin was heated in 80 °C water bath for 0, 30, 60, 120, 180, 240, 300 min. Compared with control group, Equal and Treble deferiprone group confirmed that free iron was the main oxidizing substance. Moreover, adding exogenous heme caused slight increase of meat oxidation (p < 0.05). At the same time, the antioxidant properties of deferiprone were also evaluated and it shows few antioxidant properties. This study also found that the oxidation of lipid by free iron was more serious than protein. These results suggested that controlling free iron and production of free iron from heme is a potential approach for reducing the oxidative damage of lipid and protein in meat cooking.

The oxidative reactivity of three manganese(III) porphyrin complexes with hydrogen peroxide and nitrite toward catalytic nitration of protein tyrosine

Understanding the toxicological properties of MnIII-porphyrins (MnTPPS, MnTMPyP, or MnTBAP) can provide important biochemical rationales in developing them as the therapeutic drugs against protein tyrosine nitration-induced inflammation diseases. Here, we present a comprehensive understanding of the pH-dependent redox behaviors of these MnIII-porphyrins and their structural effects on catalyzing bovine serum albumin (BSA) nitration in the presence of H2O2 and NO2-. It was found that both MnTPPS and MnTBAP stand out in catalyzing BSA nitration at physiologically close condition (pH 8), yet they are less effective at pH 6 and 10. MnTMPyP was shown to have no ability to catalyze BSA nitration under all tested pHs (pH 6, 8, and 10). The kinetics and active intermediate determination through electrochemistry method revealed that both the pH-dependent redox behavior of the central metal cation and the antioxidant capability of porphin derivative contribute to the catalytic activities of three MnIII-porphyrins in BSA nitration in the presence of H2O2/NO2-. These comprehensive studies on the oxidative reactivity of MnIII-porphyrins toward BSA nitration may provide new clues for searching the manganese-based therapeutic drugs against the inflammation-related diseases.

Structure effect of water-soluble iron porphyrins on catalyzing protein tyrosine nitration in the presence of nitrite and hydrogen peroxide

Water-soluble iron porphyrins, such as FeTPPS (5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III)), FeTMPyP (5,10,15,20-tetrakis (N-methyl-4'-pyridyl) porphyrinato iron (III) chloride) and FeTBAP (5,10,15,20-tetrakis (4-benzoic acid) porphyrinato iron (III)), are highly active catalysts for peroxynitrite decomposition and thereby have been suggested as therapeutic agent for inflammatory diseases that implicate the involvement of nitrotyrosine formation. Here, we systemically investigated catalytic properties of FeTPPS, FeTMPyP and FeTBAP on protein nitration in the presence of hydrogen peroxide and nitrite. We showed that FeTPPS, FeTBAP and FeTMPyP all exhibited higher peroxidase activity in compared with hemin. As to protein nitration, the catalytic effect of FeTPPS and FeTBAP are effective in the presence of hydrogen peroxide and nitrite, while negligible BSA nitration was observed in the case of FeTMPyP. Moreover, the underlying mechanism of the oxidation of FeTPPS, FeTBAP and FeTMPyP was further studied. Collectively, our results suggest that, compound I and II species are involved in as the key intermediates in FeTMPyP/H₂O₂ system as similar as those in FeTPPS/H₂O₂ and FeTBAP/H₂O₂ system. As compared to weak antioxidants, TPPS and TBAP, however, TMPyP scavenges oxo-Fe (IV) intermediates of FeTMPyP at a faster rate by significant self-degradation; results in the shortest lifetimes of OFe^IV-TMPyP and the lowest catalytic activity on oxidizing tyrosine and nitrite; and therefore, attributes to inactivation of FeTMPyP in protein nitration. In addition, association of FeTMPyP to BSA was found weak, while strong binding of FeTPPS and FeTBAP were observed. The weak binding keeps away of target residue of BSA from the center of FeTMPyP where the RNS is generated, which might be attributed as additional factors to the inactivation of FeTMPyP in protein nitration.

Interaction of glyceraldehyde-3-phosphate dehydrogenase and heme: The relevance of its biological function

GAPDH was speculated to function as a transient trap to reduce the potential toxicity of free heme by a specific and reversible binding with heme. Up to now, there has been lack of studies focused on this effect. In this paper, the efficiency of GAPDH-heme complex on catalyzing protein carbonylation and nitration, the cross-linking of heme to protein formation, and cytotoxicity of GAPDH-heme were studied. It was found that the binding of GAPDH could inhibit H₂O₂-mediated degradation of heme. Peroxidase activity of GAPDH-heme complex was higher than that of free heme, but significantly lower than that of HSA-heme. Catalytic activity of heme corresponded complex toward tyrosine oxidation/nitration was decreased in the order of HSA-heme, heme and GAPDH-heme. GAPDH also inhibited heme-H₂O₂-NO₂^- induced protein carbonylation. No covalent bond was formed between heme and GAPDH after treated with H₂O₂. GAPDH was more effective than HSA on protecting cells against heme-NO₂^--H₂O₂ induced cytotoxicity. These results indicate that binding of GAPDH inhibits the activity of heme in catalyzing tyrosine nitration and protects the coexistent protein against oxidative damage, and the mechanism is different from that of HSA. This study may help clarifying the protective role of GAPDH acting as a chaperone in heme transfer to downstream areas.

Nitroxides catalytically inhibit nitrite oxidation and heme inactivation induced by H2O2, nitrite and metmyoglobin or methemoglobin

Stable nitroxide radicals have multiple biological effects, although the mechanisms underlying them are not fully understood. Their protective effect against oxidative damage has been mainly attributed to scavenging deleterious radicals, oxidizing reduced metal ions and reducing oxyferryl centers of heme proteins. Yet, the potential of nitroxides to protect heme proteins against inactivation while suppressing or enhancing their catalytic activities has been largely overlooked. We have studied the effect of nitroxides, including TPO (2,2,6,6-tetramethylpiperidin-N-oxyl), 4-OH-TPO, 4-oxo-TPO and 3-carbamoyl proxyl, on the peroxidase-like activity of metmyoglobin (MbFe^III) and methemoglobin (HbFe^III) using nitrite as an electron donor by following heme absorption, H₂O₂ consumption, O₂ evolution and nitrite oxidation. The results demonstrate that the peroxidase-like activity is accompanied by a progressive heme inactivation where MbFe^III is far more resistant than HbFe^III. Nitroxides convert the peroxidase-like activity into catalase-like activity while inhibiting heme inactivation and nitrite oxidation in a dose-dependent manner. The nitroxide facilitates H₂O₂ dismutation, yet none of its reactions with any of the intermediates formed in these systems is rate-determining, and therefore its effect on the rate of the catalysis is hardly dependent on the kind of the nitroxide derivative and its concentration. The nitroxide at µM concentrations range catalytically inhibits nitrite oxidation, and consequently prevents tyrosine nitration induced by heme protein/H₂O₂/nitrite due to its fast oxidation by ^•NO₂ forming the respective oxoammonium cation, which is reduced back to the nitroxide by H₂O₂ and by superoxide radical. The nitroxides are superior over common antioxidants, which their reaction with ^•NO₂ always yields secondary radicals leading eventually to consumption of the antioxidant. A mechanism is proposed, and the kinetic simulations fit very well the experimental data in the case of MbFe^III where most of the rate constants of the reactions involved are independently known.

Metal-catalyzed protein tyrosine nitration in biological systems

Protein tyrosine nitration is an oxidative postranslational modification that can affect protein structure and function. It is mediated in vivo by the production of nitric oxide-derived reactive nitrogen species (RNS), including peroxynitrite (ONOO(-)) and nitrogen dioxide ((•)NO₂). Redox-active transition metals such as iron (Fe), copper (Cu), and manganese (Mn) can actively participate in the processes of tyrosine nitration in biological systems, as they catalyze the production of both reactive oxygen species and RNS, enhance nitration yields and provide site-specificity to this process. Early after the discovery that protein tyrosine nitration can occur under biologically relevant conditions, it was shown that some low molecular weight transition-metal centers and metalloproteins could promote peroxynitrite-dependent nitration. Later studies showed that nitration could be achieved by peroxynitrite-independent routes as well, depending on the transition metal-catalyzed oxidation of nitrite (NO₂(-)) to (•)NO₂ in the presence of hydrogen peroxide. Processes like these can be achieved either by hemeperoxidase-dependent reactions or by ferrous and cuprous ions through Fenton-type chemistry. Besides the in vitro evidence, there are now several in vivo studies that support the close relationship between transition metal levels and protein tyrosine nitration. So, the contribution of transition metals to the levels of tyrosine nitrated proteins observed under basal conditions and, specially, in disease states related with high levels of these metal ions, seems to be quite clear. Altogether, current evidence unambiguously supports a central role of transition metals in determining the extent and selectivity of protein tyrosine nitration mediated both by peroxynitrite-dependent and independent mechanisms.