Lactoferrin activates plasma membrane oxidase and Na+/H+ antiport activity

Self-assembled amphiphilic zein-lactoferrin micelles for tumor targeted co-delivery of rapamycin and wogonin to breast cancer

Protein-based micelles have shown significant potential for tumor-targeted delivery of anti-cancer drugs. In this light, self-assembled nanocarriers based on GRAS (Generally recognized as safe) amphiphilic protein co-polymers were synthesized via carbodiimide coupling reaction. The new nano-platform is composed of the following key components: (i) hydrophobic zein core to encapsulate the hydrophobic drugs rapamycin (RAP) and wogonin (WOG) with high encapsulation efficiency, (ii) hydrophilic lactoferrin (Lf) corona to enhance the tumor targeting, and prolong systemic circulation of the nanocarriers, and (iii) glutaraldehyde (GLA)-crosslinking to reduce the particle size and improve micellar stability. Zein-Lf micelles showed relatively rapid release of WOG followed by slower diffusion of RAP from zein core. This sequential release may aid in efflux pump inhibition by WOG thus sensitizing tumor cells to RAP action. Interestingly, these micelles showed good hemocompatibility as well as enhanced serum stability owing to the brush-like architecture of Lf shell. Moreover, this combined nano-delivery system maximized synergistic cytotoxicity of RAP and WOG in terms of tumor inhibition in MCF-7 breast cancer cells and Ehrlich ascites tumor animal model as a result of enhanced active targeting. Collectively, GLA-crosslinked zein-Lf micelles hold great promise for combined RAP/WOG delivery to breast cancer with reduced drug dose, minimized side effects and maximized anti-tumor efficacy.

Sirtuin activation: a role for plasma membrane in the cell growth puzzle

For more than 20 years, the observation that impermeable oxidants can stimulate cell growth has not been satisfactorily explained. The discovery of sirtuins provides a logical answer to the puzzle. The NADH-dependent transplasma membrane electron transport system, which is stimulated by growth factors and interventions such as calorie restriction, can transfer electrons to external acceptors and protect against stress-induced apoptosis. We hypothesize that the activation of plasma membrane electron transport contributes to the cytosolic NAD(+) pool required for sirtuin to activate transcription factors necessary for cell growth and survival.

The oxidative function of diferric transferrin

There is evidence for an unexpected role of diferric transferrin as a terminal oxidase for the transplasma membrane oxidation of cytosolic NADH. In the original studies which showed the reduction of iron in transferrin by the plasma membranes NADH oxidase, the possible role of the reduction on iron uptake was emphasized. The rapid reoxidation of transferrin iron under aerobic conditions precludes a role for surface reduction at neutral pH for release of iron for uptake at the plasma membrane. The stimulation of cytosolic NADH oxidation by diferric transferrin indicates that the transferrin can act as a terminal oxidase for the transplasma membrane NADH oxidase or can bind to a site which activates the oxidase. Since plasma membrane NADH oxidases clearly play a role in cell signaling, the relation of ferric transferrin stimulation of NADH oxidase to cell control should be considered, especially in relation to the growth promotion by transferrin not related to iron uptake. The oxidase can also contribute to control of cytosolic NAD concentration, and thereby can activate sirtuins for control of ageing and growth.

Plasma membrane redox and control of sirtuin

We consider possible contributions of plasma membrane redox systems to Aging control by sirtuin (SIR). Reported changes in plasma membrane redox introduced by calorie restriction (CR) may lead to activation of SIR. The most obvious effect would lie in the increase of NAD+ as a result of NADH oxidation. So the question arises, do the observed changes herald an increase in NADH oxidase under CR? The other possibility is an increase in expression of SIR by activation of plasma membrane oxidase. Previous experiments have shown that activation of the plasma membrane redox system can increase cellular NAD+ concentration. The plasma membrane redox systems are also involved in control of protein kinase activity through oxygen radical generation. This activity may be related to control of SIR expression.

Essential metal ions alter the lactoferrin binding to the erythrocyte plasma membrane receptors

The effect of metal ions at a concentration of 10(-8) to 10(-5) M [using their salts: ZnCl2, CdCl2, LiCl, CuSO4, NiSO4, Al2(SO4)3, (NH4)2MoO4 on the lactoferrin (Lf) binding to the erythrocyte membrane receptors was studied. In the absence of metal ions, Scatchard's analysis showed the existence of two kinds of binding site: one with high affinity and low capacity, and the another with low affinity and high capacity. All these metals, excluding Zn2+ and Cd2+, at a concentration 10(-5) M decreased the affinity of Lf binding (Ka1) to the high-affinity receptors. In the presence of Zn2+ and Cd2+, only the low-affinity binding site was found. Significant inhibition on the affinity (Ka2) of the low-affinity class of receptors showed Zn2+, Al3+, and Mo6+. Depending on their concentration (10(-8)-10(-5) M), these ions enhanced to a different extent, the binding capacity of the both types receptors, but the effect did not correspond to the applied doses. Several explanations of the mechanism for influence of the metal ions on the Lf-receptor interaction is discussed.

Effect of lactoferrin on the phagocytic activity of polymorphonuclear leucocytes isolated from blood of patients with autoimmune diseases and Staphylococcus aureus allergy

Phagocytic number (PN) and phagocytic index (PI) of neutrophils isolated from blood of patients with autoimmune diseases, allergy to Staphylococcus aureus and from blood of healthy individuals were examined. Our results concerning the influence of lactoferrin (Lf); (6.7 mg/l) on the PI of PMN showed that: 1) Lf enhances reliable PI of PMN at the 30-th minute starting the phagocytic reaction in patients with autoimmune disease in an active stage, in blood donors treated as healthy with the presence of autoantibodies, in patients with autoimmune diseases and proved autoantibodies against tissue, cell antigens and collagen, 2) Lf influences non-significantly PI of PMN in patients with autoimmune collagen diseases in remission, 3) Lf increases PI of PMN with 19% only in 58% from the assessed patients with Staphylococcus aureus, and 4) Lf decreases non-significantly PI of PMN in the healthy controls. Our studies on the effect of Lf on the phagocytic activity of PMN suggest that Lf has stronger effect on the PN compared to the PI: 1) Lf enhances with 86% the PN in patients with Staphylococcus aureus, 2) Lf increases PN of PMN in all of the assessed patients with autoimmune collagen diseases in active stage (mean with 72%), and 3) Lf increases PN of PMN in 4 from the 5 investigated healthy controls (mean with 22%). Our results show a "corrective" effect of Lf on the phagocytic functions in the investigated groups of patients. The possible mechanisms, by which Lf increases PN and PI of neutrophils, is discussed: 1) they may concern the antioxidative properties of Lf to block the iron ions in their catalytic inactive form or to take part as ferric-Lf in an oxidative-reduction processes on the plasma membrane and controlling transmembrane transport systems, 2) Lf decreases the negative surface charge and thus enhances the adherent ability of the PMN. Probably to this stimulated adherent ability dues the increased ingestion of bacteria in the presence of Lf, and 3) The "changed" membrane of PMN may have higher number receptors for Lf to bind more molecules of exogenous Lf. The increase of Lf binding which enhances the adherence and aggregation of neutrophils, facilitates the phagocytosis.

The plasma membrane NADH-diaphorase is active during selective phases of the cell cycle in mouse neuroblastoma cell line NB41A3. Its relation to cell growth and differentiation

Plasma membrane oxidoreductases have been described in all cells and use extracellular impermeant electron acceptors (DCIP, Ferricyanide) that are reduced by NADH. They appear to regulate the overall cell activity in response to oxidative stress from the cellular environment. An NADH-DCIP reductase has been described at the plasma membrane of NB41A3, a neuroblastoma cell line (Zurbriggen and Dryer (1993) Biochim. Biophys. Acta 1183, 513-520) whose activation with extracellular impermeant substrates promotes cell growth. Elutriation was performed to separate cells and the various fractions were analysed for enzyme activity on intact cells combined with flow cytometry. These studies showed that the enzyme is mostly induced and activated during the G1 and during the G2/M-phases. These observations were further corroborated with specific inhibitors of the cell cycle. A three-fold increase in enzyme activity was observed in the presence of alpha-amanitin, a specific cell cycle inhibitor of the G1-phase. Taxol, a specific inhibitor of the M-phase, also induces a significant increase in enzyme activity. FACS analysis of taxol -treated and alpha-amanitin-treated cells corroborated these data. The cells have been synchronized and the enzyme activity was measured at different time intervals. An activity increase was observed after ca. 2-3 h, that corresponds to a raise in the M-phase, according to FACS data. Furthermore, NTera-2 cells - a human neuroblastoma cell line that differentiates into fully mature neurones in the presence of retinoic acid - exhibit a 50% decrease in the enzyme activity during the G0-phase upon differentiation, compared to undifferentiated cells. Together the data presented in this paper show that this plasma membrane NADH-diaphorase affects cell growth and differentiation and is strongly modulated at various phases of the cell cycle.

Further evidence of different lactoferrin and transferrin binding sites on human HT29-D4 cells. Effects of lysozyme, fucose and cathepsin G. Comparison with transferrin

We have defined by using competition experiments the nature of specific lactoferrin binding sites, probably responsible for the previously observed stimulatory growth effect of the iron binding protein on HT29-D4 cells. Lysozyme, albumin and fucose do not affect lactoferrin binding showing that the binding of the protein is mediated neither by electrostatic forces nor by fucose. Iron-free and iron-loaded protein produce similar effects, demonstrating that the metal is not involved in the protein recognition. Similar results are observed for transferrin. A specific binding inhibition of lactoferrin by cathepsin G, a leukocyte proteinase, is observed, suggesting the existence of a common receptor for lactoferrin and cathepsin G on HT29-D4 cells. These results and the fact that tumor tissues are more often infiltrated by inflammatory cells such as polymorphonuclear leukocytes could evoke an unexpected role for leukocytes, possibly mediated in part by these two proteins, on the proliferative cancer effect.

Lactoferrin binding to human platelets

1. Platelets bind specifically lactoferrin. 2. The lactoferrin binding to the platelets depends on the concentration of labelled lactoferrin, the number of platelets, the time of incubation and pH. 3. The binding was characterized by two types of binding site: one with high affinity and low capacity, and another with low affinity and high capacity (respectively Kaff1 = 13.6 x 10(9) l/mol and about 40 binding sites, and Kaff2 = 1.23 x 10(9) l/mol and about 135 binding sites per platelet). 4. Both human transferrin and bovine lactoferrin compete with human lactoferrin for the receptors. 5. The presence of lactoferrin receptors on the platelet membrane surface is connected most probably with the effect(s) on the cell function(s) of these cells.

Characterization of the anti-cancer activity of transferrin-adriamycin conjugates

The anthracycline anti-cancer drug adriamycin (Adr) was coupled to human transferrin (Trf) by using a glutaraldehyde technique. The effect of Trf-Adr conjugates and unconjugated Adr on human cells was determined by using normal peripheral blood mononuclear cells and chronic myelogenous K562 cells. Cytotoxicity was determined by using an assay that measures the conversion of a tetrazolium salt (MTT) into a purple product (formazan) by mitochondrial dehydrogenases in viable cells. We found that free Adr at a concentration of 1 x 10(-7) had little effect on K562 cells, while Trf-Adr conjugates inhibited 75% of cellular activity. When normal peripheral blood mononuclear cells were tested against Trf-Adr conjugates, the 50% inhibitory concentration was found to be 1.4-1.7 x 10(-6) M, at which concentration greater than 85% of K562 cells were inhibited. Interactions of Trf-Adr conjugates with plasma membrane energy-producing systems are the proposed mechanisms of cytotoxicity.