Heme Iron Release Research Articles

Sulfmyoglobin production by free cysteine during thermal treatment: Involvement of heme iron in the production of free radicals

The meat greening is an abnormal pigmentation related to microbiological contamination and lipid oxidation during storage. This color change results from sulfmyoglobin (SulfMb) production promoted by the reaction between metmyoglobin (MetMb), H2O2, and thiol compounds. Spectral studies on cooked meat suggested the production of SulfMb, probably due to the increment of free radicals during thermal treatment. Thus, we evaluated the involvement of free radicals and heme iron in the SulfMb production from horse MetMb and free cysteine (Cys) during thermal treatment. The results confirm that the reaction of SulfMb production at meat muscle pH (5.7–7.2) during heat treatment is a product of free radicals formed from Cys oxidation (SH) and reactive oxygen species (O2−, H2O2). This is catalyzed by the release of heme iron, thus promoting a consecutive reaction having MbFe(IV)O as a reaction intermediate.

Heme Iron Release from Alginate Beads at In Vitro Simulated Gastrointestinal Conditions

Heme iron (Fe) release from alginate beads at in vitro simulated gastrointestinal conditions for potential use as oral heme Fe supplement was studied. Five beads at different ratios of sodium alginate (SA)-to-spray-dried bovine blood cells (SDBC) with weight ratios of 1:1.25, 1:2.5, 1:5, 1:10, and 1:15 (w/w) were prepared. Release characteristics of these beads were investigated at in vitro simulated gastrointestinal conditions. Release media pH strongly influenced the controlled Fe release from the beads. The heme Fe-beads in simulated gastric fluid (pH 2) remained in a shrinkage state and Fe release was low: 25.8, 21.1, 11.6, 12.1, and 12.0% for 1:1.25, 1:2.5, 1:5, 1:10, and 1:15 ratios, respectively. Proportion and amount of Fe released by 1:1.25 and 1:2.5 ratios was higher than the other ratios. The heme Fe-beads swelled and dissociated in simulated intestinal fluid (pH 6), releasing three-fourths of the Fe in 200min. The morphology studies showed that Fe release followed formation of pores in the alginate matrix, generating erosion of the beads and complete disintegration after 75 and 200min of gastric and intestinal incubation, respectively. These results indicate that heme Fe-beads may be useful for oral delivery of heme Fe supplement.

Formation of Fluorescent Heme Degradation Products during the Oxidation of Hemoglobin by Hydrogen Peroxide

Hemoglobin and methemoglobin oxidized by hydrogen peroxide generate ferrylhemoglobin and oxoferrylhemoglobin, respectively. Two fluorescent compounds were found to be produced during the reaction of oxyhemoglobin, but not methemoglobin, with H 2O 2. These two compounds had excitation wavelengths of 321 nm and 460 nm, respectively, with emission wavelengths of 465 nm and 525 nm, respectively. The formation of the same fluorescent products during the reaction of H 2O 2with ferroprotoporphyrin-IX and ferriprotoporphyrin-IX demonstrate that these compounds originate from the heme moiety. The release of heme iron during the formation of these fluorescent compounds indicates that they are associated with heme degradation. The time course for the formation of fluorescent products show that the extent of heme degradation is dependent on H 2O 2concentration. The results of this investigation indicate that the heme moiety of Fe(II) hemoglobin undergoes degradation in presence of H 2O 2. The ability to detect this process by fluorescence provides a sensitive marker in order to asses hemoglobin and RBC oxidative stress under pathological conditions.

Hemin: a possible physiological mediator of low density lipoprotein oxidation and endothelial injury.

Oxidized low density lipoprotein (LDL), formed in vivo from presently unknown reactions, may play a role in atherogenesis. In vitro, transition metals such as iron and copper will facilitate LDL oxidation, but these metals are unlikely to exist in free form in normal body fluids. We have explored the possibility that LDL oxidation may be promoted by heme, a physiologically ubiquitous, hydrophobic, iron-containing compound. Indeed, during several-hour incubation, heme caused extensive oxidative modification of LDL; however, such modification requires only minutes in the presence of small amounts of H2O2 or preformed lipid hydroperoxides within the LDL. Oxidative interactions between heme, LDL, and peroxides lead to degradation of the heme ring and consequent release of heme iron, which further accelerates heme degradation. Coupled (evidently iron-catalyzed) heme degradation and LDL oxidation are both effectively inhibited by hydrophobic antioxidants and iron chelators. That such hemin-induced LDL oxidation may be involved in atherogenesis is supported by the finding that LDL oxidized by hemin is extremely cytotoxic to cultured aortic endothelial cells. Overall, these investigations not only lend support to the idea that LDL oxidation by physiological substances such as heme may play a role in the process of atherogenesis but also may have broader implications, as similar oxidative reactions between heme and unsaturated fatty acids may occur consequent to hemorrhagic injury.

Cytochrome c-catalyzed membrane lipid peroxidation by hydrogen peroxide

Cytochrome c 3+ -catalyzed peroxidation of phosphatidylcholine liposomes by hydrogen peroxide (H 2O 2) was indicated by the production of thiobarbituric acid reactive substances, oxygen consumption, and emission of spontaneous chemiluminescence. The iron chelator diethylenetriaminepentaacetic acid (DTPA) only partially inhibited peroxidation when H 2O 2 concentrations were 200 μ m or greater. In contrast, iron compounds such as ferric chloride, potassium ferricyanide, and hemin induced H 2O 2-dependent lipid peroxidation which was totally inhibitable by DTPA. Cyanide and urate, which react at or near the cytochrome—heme, completely prevented lipid peroxidation, while hydroxyl radical scavengers and superoxide dismutase had very little or no inhibitory effect. Changes in liposome surface charge did not influence cytochrome c 3+ plus H 2O 2-dependent peroxidation, but a net negative charge was critical in favoring cytochrome c 3+ -dependent, H 2O 2-independent lipid auto-oxidative processes. These results show that reaction of cytochrome c with H 2O 2 promotes membrane oxidation by more than one chemical mechanism, including formation of high oxidation states of iron at the cytochrome—heme and also by heme iron release at higher H 2O 2 concentrations. Cytochrome c 3+ could react with mitochondrial H 2O 2 to yield “site-specific” mitochondrial membrane lipid peroxidation during tissue oxidant stress.