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This study demonstrates that heme peroxidases from different superfamilies react differently with chlorite. In contrast to plant peroxidases, like horseradish peroxidase (HRP), the mammalian counterparts myeloperoxidase (MPO) and lactoperoxidase (LPO) are rapidly and irreversibly inactivated by chlorite in the micromolar concentration range. Chlorite acts as efficient one-electron donor for Compound I and Compound II of MPO and LPO and reacts with the corresponding ferric resting states in a biphasic manner. The first (rapid) phase is shown to correspond to the formation of a MPO-chlorite high-spin complex, whereas during the second (slower) phase degradation of the prosthetic group was observed. Cyanide, chloride and hydrogen peroxide can block or delay heme bleaching. In contrast to HRP, the MPO/chlorite system does not mediate chlorination of target molecules. Irreversible inactivation is shown to include heme degradation, iron release and decrease in thermal stability. Differences between mammalian peroxidases and HRP are discussed with respect to differences in active site architecture and heme modification.

During the immune response, the cytokine interleukin 8 (IL-8, CXCL8) functions as a strong chemoattractant for polymorphonuclear leukocytes helping to direct these cells to infected/injured sites. This review focuses on the interaction of IL-8 with sulfated glycosaminoglycans expressed on cell surfaces and the extracellular matrix. This interaction contributes to the recruitment of polymorphonuclear cells from blood, penetration of these cells through the vessel wall, and their directed migration to inflammatory sites. Regulatory aspects of the interplay between IL-8 and heparan sulfate, the most abundant glycosaminoglycan, are highlighted. In this field, the large natural heterogeneity of glycosaminoglycans represents a great challenge that impedes the modeling of IL-8 functions. The interaction of IL-8 with newly developed artificial sulfated hyaluronan derivatives is also considered as these artificial substrates are an important tool for development of new materials in regenerative medicine.

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On the basis of these data, different strategies to further optimize LPO functions in humoral defense of mucous surfaces and biotechnological applications are discussed. In particular, hydrophobic organic substrates with a 3,4-dihydroxyphenyl partial structure considerably enhance the (pseudo-)halogenating activity of LPO. Their application provides, thus, a new strategy to enhance the anti-microbial activity of this enzyme.

In the presence of hydrogen peroxide, the heme protein lactoperoxidase is able to oxidize thiocyanate and iodide to hypothiocyanite, reactive iodine species, and the inter(pseudo)halogen cyanogen iodide. The killing efficiency of these oxidants and of the lactoperoxidase-HO-SCN/I system was investigated on the bioluminescent Escherichia coli K12 strain that allows time-resolved determination of cell viability. Among the tested oxidants, cyanogen iodide was most efficient in killing E. coli, followed by reactive iodine species and hypothiocyanite. Thereby, the killing activity of the LPO-HO-SCN/I system was greatly enhanced in comparison to the sole application of iodide when I was applied in two- to twenty-fold excess over SCN. Further evidence for the contribution of cyanogen iodide in killing of E. coli was obtained by applying methionine. This amino acid disturbed the killing of E. coli mediated by reactive iodine species (partial inhibition) and cyanogen iodide (total inhibition), but not by hypothiocyanite. Changes in luminescence of E. coli cells correlate with measurements of colony forming units after incubation of cells with the LPO-HO-SCN/I system or with cyanogen iodide. Taken together, these results are important for the future optimization of the use of lactoperoxidase in biotechnological applications.

Excessive release of hemoglobin from red blood cells markedly disturbs the health status of patients due to cytotoxic effects of free hemoglobin and heme. The latter component is able to initiate novel hemolytic events in unperturbed red blood cells. We modeled this process by incubation of ferric protoporphyrin IX with freshly isolated red blood cells from healthy volunteers. The heme-induced hemolysis was inhibited in a concentration-dependent manner by the chlorite-based drug WF10, whereby the hemolysis degree was totally abolished at a molar ratio of 1:2 between chlorite and heme. Upon incubation of heme with WF10, the ultraviolet-visible spectrum changed, whereas the release of iron from heme and the appearance of fluorescent breakdown products of the porphyrin ring were negligible at this ratio, but increased with increasing excess of chlorite over heme. Thus, inhibition of hemolysis by WF10 takes already place at those chlorite concentrations, where no degradation of the porphyrin ring occurs. As WF10 is applied in form of an intravenous infusion to patients with severe inflammatory states, these data support the hypothesis that the beneficial WF10 effects are closely associated with inactivation of free heme.