Molecular mimicry of the receptor-binding domain of the SARS-CoV-2 spike protein: from the interaction of spike-specific antibodies with transferrin and lactoferrin to the antiviral effects of human recombinant lactoferrin.

The pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection involves dysregulations of iron metabolism, and although the mechanism of this pathology is not yet fully understood, correction of iron metabolism pathways seems a promising pharmacological target. The previously observed effect of inhibiting SARS-CoV-2 infection by ferristatin II, an inducer of transferrin receptor 1 (TfR1) degradation, prompted the study of competition between Spike protein and TfR1 ligands, especially lactoferrin (Lf) and transferrin (Tf). We hypothesized molecular mimicry of Spike protein as cross-reactivity of Spike-specific antibodies with Tf and Lf. Thus, strong positive correlations (R2 > 0.95) were found between the level of Spike-specific IgG antibodies present in serum samples of COVID-19-recovered and Sputnik V-vaccinated individuals and their Tf-binding activity assayed with peroxidase-labeled anti-Tf. In addition, we observed cross-reactivity of Lf-specific murine monoclonal antibody (mAb) towards the SARS-CoV-2 Spike protein. On the other hand, the interaction of mAbs produced to the receptor-binding domain (RBD) of the Spike protein with recombinant RBD protein was disrupted by Tf, Lf, soluble TfR1, anti-TfR1 aptamer, as well as by peptides RGD and GHAIYPRH. Furthermore, direct interaction of RBD protein with Lf, but not Tf, was observed, with affinity of binding estimated by KD to be 23 nM and 16 nM for apo-Lf and holo-Lf, respectively. Treatment of Vero E6 cells with apo-Lf and holo-Lf (1-4 mg/mL) significantly inhibited SARS-CoV-2 replication of both Wuhan and Delta lineages. Protective effects of Lf on different arms of SARS-CoV-2-induced pathogenesis and possible consequences of cross-reactivity of Spike-specific antibodies are discussed.

Erythropoietin and Nrf2: key factors in the neuroprotection provided by apo-lactoferrin.

Among the properties of lactoferrin (LF) are bactericidal, antianemic, immunomodulatory, antitumour, antiphlogistic effects. Previously we demonstrated its capacity to stabilize in vivo HIF-1-alpha and HIF-2-alpha, which are redox-sensitive multiaimed transcription factors. Various tissues of animals receiving recombinant human LF (rhLF) responded by expressing the HIF-1-alpha target genes, hence such proteins as erythropoietin (EPO), ceruloplasmin, etc. were synthesized in noticeable amounts. Among organs in which EPO synthesis occurred were brain, heart, spleen, liver, kidneys and lungs. Other researchers showed that EPO can act as a protectant against severe brain injury and status epilepticus in rats. Therefore, we tried rhLF as a protector against the severe neurologic disorders developed in rats, such as the rotenone-induced model of Parkinson's disease and experimental autoimmune encephalomyelitis as a model of multiple sclerosis, and observed its capacity to mitigate the grave symptoms. Moreover, an intraperitoneal injection of rhLF into mice 1 h after occlusion of the medial cerebral artery significantly diminished the necrosis area measured on the third day in the ischaemic brain. During this period EPO was synthesized in various murine tissues. It was known that EPO induces nuclear translocation of Nrf2, which, like HIF-1-alpha, is a transcription factor. In view that under conditions of hypoxia both factors demonstrate a synergistic protective effect, we suggested that LF activates the Keap1/Nrf2 signaling pathway, an important link in proliferation and differentiation of normal and malignant cells. J774 macrophages were cultured for 3 days without or in the presence of ferric and ferrous ions (RPMI-1640 and DMEM/F12, respectively). Then cells were incubated with rhLF or Deferiprone. Confocal microscopy revealed nuclear translocation of Nrf2 (the key event in Keap1/Nrf2 signaling) induced by apo-rhLF (iron-free, RPMI-1640). The reference compound Deferiprone (iron chelator) had the similar effect. Upon iron binding (in DMEM/F12) rhLF did not activate the Keap1/Nrf2 pathway. Added to J774, apo-rhLF enhanced transcription of Nrf2-dependent genes coding for glutathione S-transferase P and heme oxygenase-1. Western blotting revealed presence of Nrf2 in mice brain after 6 days of oral administration of apo-rhLF, but not Fe-rhLF or equivalent amount of PBS. Hence, apo-LF, but not holo-LF, induces the translocation of Nrf2 from cytoplasm to the nucleus, probably due to its capacity to induce EPO synthesis.

Modifying effects of lactoferrin in vitro on molecular phenotype of human breast cancer cells.

AIM: To assess the role of endogenous lactoferrin (LF) in the formation of the molecular phenotype of human breast cancer (BC) cell lines with varying degrees of malignancy, including cisplatin/doxorubicin resistant cell lines, and identify possible impact of exogenous LF. MATERIALS AND METHODS: 5 breast cell lines of different origin - MCF-10 A, MCF-7, including doxorubicin/cisplatin resistant ones, T47D, MDA-MB-231, and MDA-MB-468. Immunocytochemistry: expression of LF, Ki-67, adhesion molecules E- and N-cadherin, CD44, CD24 rating the invasive potential of cells. RESULTS: Expression of LF in human BC cell lines varies. It is associated with the heterogeneity of molecular profiles of cell lines in terms of adhesion. A link has been established between the level of LF expression in the resistant cell line MCF-7/CP and MCF-7/Dox, features of their molecular profile and invasive properties. Exogenous LF was shown to be capable of modifying the molecular profile and invasive properties of all the studied cell lines including resistant ones (MCF-7/CP and MCF-7/Dox). CONCLUSIONS: The sensitivity of cytostatic-resistant cell lines (MCF-7/CP and MCF-7/Dox) tends to increase under the influence of exogenous LF. It is likely that this effect is due to LF-mediated inhibition of the expression of proteins associated with drug resistance.

The functional state of the xenobiotic metabolizing system in rat liver following chronic administration of diethylnitrosamine or its precursors.

The effect of chronic administration of 0.002% N-nitrosodiethylamine (DENA), 0.002% diethylamine (DEA) and 0.0005% sodium nitrite (SN) on the functional state of the xenobiotic metabolizing system in rat liver was investigated. Administration of DEA and DENA increased concentration of cytochromes P-450 and b5. SN did not affect the enzymes of the monooxygenase system. Coadministration of DEA and SN maximally increased the concentration of cytochrome P-450. It is not possible to explain the phenomenon of combined administration of SN and DEA by simple summation of the effects caused by them separately. The activity of microsomal glutathione S-transferase did not change when DEA and SN were given together, yet increased when they were administered separately. The maximum increase of the total activity of cytosol glutathione S-transferases was observed following DENA. In all four experimental groups a decrease of isoenzyme 5-5 activity was observed. Investigation of Se-independent glutathione peroxidase activity showed the multivariance of response of the glutathione S-transferase family to the compounds studied. The concentration of hepatic free SH-groups increased following administration of DENA and decreased dramatically when SN and DEA were coadministered. When they were given separately the concentration remained at control level.

[The functional status of the xenobiotic biotransformation system in poisoning animals with diphenylamine and N-nitrosodiphenylamine]. / Funktsional'noe sostoianie sistemy biotransformatsii ksenobiotikov pri intoksikatsii zhivotnykh difenilaminom i N-nitrozodifenilaminom.

The state of the xenobiotic biotransformation system has been studied after a single per os administration of diphenylamine (DPA) and N-nitrosodiphenylamine (NDPA) to male albino rats. Intoxication of animals with NDPA induced unidirectional and similar changes in the functional states of the both stages of the xenobiotic metabolism. There was an increase in the total content of cytochrome P-450 and the activity of NADPH-cytochrome P-450 reductase as well as a marked elevation of activity of microsomal glutathione S-transferase. This was paralleled with the induction of activity of individual isoenzymes of the multifunctional family of rat liver cytosol glutathione S-transferases and increased activity of glutathione reductase. Unlike NDPA, DPA affected only the second stage of the xenobiotic biotransformation by stimulating the activity of both membrane-bound and soluble glutathione S-transferases. In both cases the intoxication was attended by an increase in the number of SH-groups unbound to the protein. It was assumed that the different response of the xenobiotic biotransformation system to DPA and NDPA may be due to the appearance of a N-nitroso group in the NDPA molecule.