H2O2-Diffusion Through Liposomes

Bioprinting of a Liposomal Oxygen-Releasing Scaffold for Ovary Tissue Engineering

This study addresses a critical challenge in bioprinting for regenerative medicine, specifically the issue of hypoxia compromising cell viability in engineered tissues. To overcome this hurdle, a novel approach using a microfluidic bioprinter is used to create a two-layer structure resembling the human ovary. This structure incorporates a liposomal oxygen-releasing system to enhance cell viability. The bioprinting technique enables the simultaneous extrusion of two distinct bioinks, namely, bioink A (comprising alginate 1% and 5 mg/mL PEGylated fibrinogen in a 20:1 molar ratio) and bioink B (containing alginate 0.5%). In addition, liposomal catalase and hydrogen peroxide (H2O2) are synthesized and incorporated into bioinks A and B, respectively. The liposomes are prepared using thin film hydration with a monodisperse size (140-160 nm) and high encapsulation efficiency. To assess construct functionality, isolated human ovarian cells are added to bioink A. The bioprinted constructs, with or without liposomal oxygen-releasing systems, are cultured under hypoxic and normoxic conditions for 3 days. Live/Dead assay results demonstrate that liposomal oxygen-releasing systems effectively preserve cell viability in hypoxic conditions, resembling viability under normoxic conditions without liposomes. PrestoBlue assay reveals significantly higher mitochondrial activity in constructs with liposomal oxygen delivery systems under both hypoxic and normoxic conditions. The evaluation of apoptosis status through annexin V immunostaining shows that liposomal oxygen-releasing scaffolds successfully protect cells from hypoxic stress, exhibiting a proportion of apoptotic cells similar to normoxic conditions. In contrast, constructs lacking liposomes in hypoxic conditions exhibit a higher incidence of cells in early-stage apoptosis. In conclusion, the study demonstrates the promising potential of bioprinted oxygen-releasing liposomal scaffolds to protect ovarian stromal cells in hypoxic environments. These innovative scaffolds not only offer protection but also recapitulate the mechanical differences between the medulla and the cortex in the normal ovary structure. This opens new avenues for advanced ovary tissue engineering and transplantation strategies.

Liposomal oxygen-generating hydrogel for enhancing cell survival under hypoxia condition

The inadequate oxygen supply to engineered tissues has been a persistent challenge in tissue engineering and regenerative medicine. To overcome this limitation, we developed a scaffold combined with an oxygen-releasing liposomal system comprising catalase-loaded liposomes (CAT@Lip) and H2O2-loaded liposomes (H2O2@Lip). This oxygenation system has shown high cytocompatibility when they were applied to human stromal cells. Under hypoxic conditions, the cell viability enclosed in the oxygen-releasing liposomal alginate hydrogel (94.62 ± 3.46 %) was significantly higher than that of cells enclosed in hydrogel without liposomes (47.18 ± 9.68 %). There was no significant difference in cell viability and apoptosis rate compared to normoxia conditions after three days, indicating the effectiveness of the oxygen-releasing approach in hypoxic conditions. In conclusion, our study demonstrates that the use of liposomal oxygen-releasing scaffolds can overcome the oxygen diffusion challenge in tissue implant fabrication, providing a simple solution for cellular oxygenation that could be a crucial element in tissue engineering.

Tumor microcalcification-mediated relay drug delivery for photodynamic immunotherapy of breast cancer

Spatiotemporal targeting of tumor-associated macrophages (TAMs) and tumor cells is emerging as a promising strategy for tumor therapy. Tumor microcalcifications that specifically bind to bisphosphonates are potentially used to design efficient relay drug delivery nanosystems to achieve spatiotemporal drug modulation. Here, we developed manganese dioxide (MnO₂)-embedded and LyP-1 peptide-labeled liposomal nanoparticles (NPs) for photodynamic immunotherapy of breast cancer; zoledronic acid (Zol) was encapsulated in the hydrophilic cavity of liposomes, and a hydrophobic photosensitizer (IR780) was embedded in the phospholipid bilayer of liposomes. These Lipo Zol/IR NPs generated O₂ bubbles through MnO₂ in response to H₂O₂ in the tumor microenvironment, leading to the degradation of the liposomal membrane, which triggered the release of Zol and provided O₂ for photodynamic therapy. The released Zol attached to microcalcifications and was selectively phagocytosed by TAMs, leading to the induction of death or repolarization of TAMs from the immunosuppressive M2 phenotype to the immunostimulatory M1 phenotype. The remaining liposomal fragments embedded with IR780 then preferentially targeted tumor cells through LyP-1 peptide and produced abundant reactive oxygen species (ROS) under near infrared (NIR) laser irradiation, resulting in the death of tumor cells and mild immune activation. All in vitro and in vivo studies demonstrated the effective photodynamic and immunoregulatory performance of Lipo Zol/IR NPs. STATEMENT OF SIGNIFICANCE: Spatiotemporal targeting of tumor-associated macrophages (TAMs) and tumor cells remains a challenge in tumor photodynamic immunotherapy for promoting synergy and reducing side effects. Here, we developed tumor microcalcification-mediated relay drug delivery nanoliposomes for breast cancer therapy. H₂O₂ in the tumor microenvironment (TME) triggers the breakage of nanoliposomes, thereby causing the separation of zoledronic acid (Zol) and the photosensitizer IR780 and allowing them to perform their respective functions. Microcalcifications enable Zol to target TAMs, resulting in immunomodulation. LyP-1 guides IR780 to target tumor cells for PDT with adequate O₂ supply. These nanoliposomes enable precise spatiotemporal targeting of different types of cells in the TME and promote the synergy between immunotherapy and PDT while ensuring the effectiveness of both methods.

Singlet Oxygen Generation in Dark-Hypoxia by Catalytic Microenvironment-Tailored Nanoreactors for NIR-II Fluorescence-Monitored Chemodynamic Therapy

Singlet oxygen (¹ O₂ ) has a potent anticancer effect, but photosensitized generation of ¹ O₂ is inhibited by tumor hypoxia and limited light penetration depth. Despite the potential of chemodynamic therapy (CDT) to circumvent these issues by exploration of ¹ O₂ -producing catalysts, engineering efficient CDT agents is still a formidable challenge since most catalysts require specific pH to function and become inactivated upon chelation by glutathione (GSH). Herein, we present a catalytic microenvironment-tailored nanoreactor (CMTN), constructed by encapsulating MoO₄ ^2- catalyst and alkaline sodium carbonate within liposomes, which offers a favorable pH condition for MoO₄ ^2- -catalyzed generation of ¹ O₂ from H₂ O₂ and protects MoO₄ ^2- from GSH chelation owing to the impermeability of liposomal lipid membrane to ions and GSH. H₂ O₂ and ¹ O₂ can freely cross the liposomal membrane, allowing CMTN with a built-in NIR-II ratiometric fluorescent ¹ O₂ sensor to achieve monitored tumor CDT.

Immune, inflammatory, autophagic and DNA damage responses to long-term H2O2 exposure in different tissues of common carp (Cyprinus carpio)

Hydrogen peroxide (H₂O₂) is a stable reactive oxygen species (ROS) in aquatic environment, and high concentration of ambient H₂O₂ may directly or indirectly affect aquatic animal health. However, the response mechanism of fish to ambient H₂O₂ has not been well studied yet. Therefore, the aim of the study was to investigate the immune, inflammatory, autophagic and DNA damage responses to long-term H₂O₂ exposure in different tissues of common carp. The results showed that H₂O₂ exposure induced a significant immune response, with alterations in the levels of immune parameters including AKP, ACP, LZM, C3, HSP90 and HSP70 in different tissues. The inflammatory response evoked by H₂O₂ exposure was associated with the activations of TLRs and NF-κB (P65) in the majority of tested tissues. The autophagy process was significantly affected by H₂O₂ exposure, evidenced by the upregulations of the autophagy-related genes in liver, gills, muscle, intestines, heart and spleen and the downregulations in kidney. Meanwhile, the mRNA level of atm, a primary transducer of DNA damage response, was upregulated in liver, gills, intestines and spleen, and the DNA damage was evidenced by increased 8-OHdG level in intestines after H₂O₂ exposure. Moreover, cell cycle regulation-related genes, including cyclin A1, B and/or E1, highly expressed in all tested tissues except heart after H₂O₂ exposure. Interestingly, IBR analysis exhibited that immune, inflammatory, autophagic and DNA damage responses to H₂O₂ exposure were in a dose-dependent and tissue-specific manner. These data may contribute to understanding H₂O₂ toxicity for fish and assessing potential risk of H₂O₂ in aquatic environment.

Self-Supplied Tumor Oxygenation through Separated Liposomal Delivery of H2O2 and Catalase for Enhanced Radio-Immunotherapy of Cancer

The recent years have witnessed the blooming of cancer immunotherapy, as well as their combinational use together with other existing cancer treatment techniques including radiotherapy. However, hypoxia is one of several causes of the immunosuppressive tumor microenvironment (TME). Herein, we develop an innovative strategy to relieve tumor hypoxia by delivering exogenous H₂O₂ into tumors and the subsequent catalase-triggered H₂O₂ decomposition. In our experiment, H₂O₂ and catalase are separately loaded within stealthy liposomes. After intravenous (iv) preinjection of CAT@liposome, another dose of H₂O₂@liposome is injected 4 h later. The sustainably released H₂O₂ could be decomposed by CAT@liposome, resulting in a long lasting effect in tumor oxygenation enhancement. As the result, the combination treatment by CAT@liposome plus H₂O₂@liposome offers remarkably enhanced therapeutic effects in cancer radiotherapy as observed in a mouse tumor model as well as a more clinically relevant patient-derived xenograft tumor model. Moreover, the relieved tumor hypoxia would reverse the immunosuppressive TME to favor antitumor immunities, further enhancing the combined radio-immunotherapy with cytotoxic T lymphocyte-associated antigen 4 (CTLA4) blockade. This work presents a simple yet effective strategy to promote tumor oxygenation via sequential delivering catalase and exogenous H₂O₂ into tumors using well-established liposomal carriers, showing great potential for clinical translation in radio-immunotherapy of cancer.

Spectrophotometric Quantification of Peroxidase with p-Phenylene-diamine for Analyzing Peroxidase-Encapsulating Lipid Vesicles

A spectrophotometric assay for the determination of horseradish peroxidase (HRP) in aqueous solution with p-phenylenediamine (PPD, benzene-1,4-diamine) as electron donor substrate and hydrogen peroxide (H2O2) as oxidant was developed. The oxidation of PPD by HRP/H2O2 leads to the formation of Bandrowski's base ((3E,6E)-3,6-bis[(4-aminophenyl)imino]cyclohexa-1,4-diene-1,4-diamine), which can be quantified by following the increase in absorbance at 500 nm. The assay was applied for monitoring the activity of HRP inside ≈180 nm-sized lipid vesicles (liposomes), prepared from POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and purified by size exclusion chromatography. Because of the high POPC bilayer permeability of PPD and H2O2, the HRP-catalyzed oxidation of PPD occurs inside the vesicles once PPD and H2O2 are added to the vesicle suspension. In contrast, if instead of PPD the bilayer-impermeable substrate ABTS2- (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) is used, the oxidation of ABTS2- inside the vesicles does not occur. Therefore, using PPD and ABTS2- in separate assays allows distinguishing between vesicle-trapped HRP and HRP in the external bulk solution. In this way, the storage stability of HRP-containing POPC vesicles was investigated in terms of HRP leakage and activity of entrapped HRP. It was found that pH 7.0 suspensions of POPC vesicles (2.2 mM POPC) containing on average about 12 HRP molecules per vesicle are stable for at least 1 month without any significant HRP leakage, if stored at 4 °C. Such high stability is beneficial not only for bioanalytical applications but also for exploring the kinetic properties of vesicle-entrapped HRP through simple spectrophotometric absorption measurements with PPD as a sensitive and cheap substrate.

Modulatory effect of fatty acids on fungicidal activity, respiratory burst and TNF-α and IL-6 production in J774 murine macrophages

The reported effects of different families of fatty acids (FA; SFA, MUFA, n-3 and n-6 PUFA) on human health and the importance of macrophage respiratory burst and cytokine release to immune defence led us to examine the influence of palmitic acid (PA), oleic acid (OA), linoleic acid, arachidonic acid, EPA and DHA on macrophage function. We determined fungicidal activity, reactive oxygen species (ROS) and cytokine production after the treatment of J774 cells with non-toxic concentrations of the FA. PA had a late and discrete stimulating effect on ROS production, which may be associated with the reduced fungicidal activity of the cells after treatment with this FA. OA presented a sustained stimulatory effect on ROS production and increased fungicidal activity of the cells, suggesting that enrichment of diets with OA may be beneficial for pathogen elimination. The effects of PUFA on ROS production were time- and dose-dependently regulated, with no evident differences between n-3 and n-6 PUFA. It was worth noting that most changes induced after stimulation of the cells with lipopolysaccharide were suppressed by the FA. The present results suggest that supplementation of the diet with specific FA, not classes of FA, might enable an improvement in host defence mechanisms or a reduction in adverse immunological reactions.

Active oxygen chemistry within the liposomal bilayer. Part IV: Locating 2',7'-dichlorofluorescein (DCF), 2',7'-dichlorodihydrofluorescein (DCFH) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in the lipid bilayer

2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) is commonly used to detect the generation of reactive oxygen intermediates and for assessing the overall oxidative stress in toxicological phenomenon. It has been suggested that DCFH-DA crosses the cell membrane, subsequently undergoing deacetylation by intracellular esterases. The resulting 2',7'-dichlorodihydrofluorescein (DCFH) is proposed to react with intracellular hydrogen peroxide or other oxidizing ROS to give the fluorescent 2',7'-dichlorofluorescein (DCF). Using an NMR chemical shift-polarity correlation, we have determined that DCFH-DA and DCFH are located well within the lipid bilayer and certainly not at the interface. These results, therefore, put into serious question the proposed ability of DCFH to come in contact with the aqueous phase and thereby interact with aqueous intracellular ROS and components. However, H2O2 and superoxide can cross or at least penetrate the lipid bilayer and react with certain lipophilic substrates. This may well describe the mode of reaction of these and other ROS with DCFH.

Leptospires are killed in vitro by both oxygen-dependent and -independent reactions

This study reports for the first time that leptospires are killed by H(2)O(2) and by low-molecular-weight primary granule components, which are agents normally released by neutrophils upon stimulation. Although both pathogenic and nonpathogenic strains were sensitive to H(2)O(2)-mediated killing, nonpathogenic organisms were found to be more susceptible. In addition, the killing of leptospires by H(2)O(2) was found to be independent of the presence of the neutrophil primary granule component myeloperoxidase and therefore not a consequence of halogenation reactions. We have also determined that leptospires are significantly sensitive only to primary granule components and, among those, to proteins and/or peptides of less than 30 kDa.

Superoxide organic chemistry within the liposomal bilayer, part II: a correlation between location and chemistry

Coumarin ester derivatives 1, substituted at C-4 and/or C-12 with alkyl chains, were synthesized and intercalated within DMPC liposomal bilayers. By correlating the 13C chemical shift with medium polarity [E(T)(30)], the relative location of these substrates within the liposomal bilayer was determined. The length of the alkyl chain substituents clearly influences the lipophilicity of the substrates and their location and orientation within the liposome: Superoxide readily saponifies the C-12 esteric linkage of 1, when this reaction site lies in a polar region of the liposome (E(T)(30) > 45 kcal/mol), to give the corresponding 7-hydroxy coumarin derivatives 2. However, when C-12 lies deeper and is hence less available to O(2)(*-), the lactonic carbon C-2, which lies in a shallower region (E(T)(30) = 43-49), is the preferred site for superoxide-mediated cleavage. When coumarin 1 is disubstituted with long chains at both C-12 and C-4, these derivatives lie deep within the bilayer and react only slowly with O(2)(*-). These results indicate there is indeed a correlation between location within the bilayer and substrate reactivity. Contrary to the suggestion of Dix and Aikens (Chem. Res. Toxicol.6:2-18; 1993) superoxide can penetrate deep within the liposomal bilayer. Nevertheless, its concentration drops precipitously (to approximately 16% of what it is near the interface) below E(T) values of 38, thereby precluding substantial reaction with many highly lipophilic substrates. This work also confirms the findings of others that reactions of small oxy-radicals occur within cellular membranes and appear to be of significant biological importance.

The positive role of voids in the plasma membrane in growth and energetics of Escherichia coli

Bacterial respiration, endogenous as well as induced respiration by glucose, lactose and glycine betaine, was found to be sensitive to external solute concentration. Permeability of hydrogen peroxide, a non-electrolyte of molecular size between water and urea, through the bacterial membranes changed directly with the rate of respiration (an activity residing in the bacterial plasma membrane) in E. coli and the enhanced permeability and respiratory activity were highly correlated. Hydrogen peroxide permeability and induction of voids (spaces in the matrix of the bilayer into which hydrophobic fluorescent probes partition, which in turn were used to assess the modulation of these cavities) were shown to be a direct and excellent measure of leak conductance. Fluorescence intensity and anisotropy of the extrinsic fluorescent probes (incorporated by growing bacteria in their presence) decreased with increased respiration in bacteria, consistent with lowered molecular restriction and enhanced hydration in the membrane phase for these probes as seen in dimyristoylphosphatidylcholine bilayers due to phase transition. The physical basis of osmotic phenomena, as a relevant (thermodynamic) volume, could relate to water exchange or compression, depending on the osmotic domain. In the domain of compression in bacteria, i.e. well above the isotonic range, the computed activation volume was consistent with voids in the membrane. This study emphasises a major role of leak conductance in bacterial physiology and growth.

Aging exacerbates hydrogen peroxide-induced alteration of vascular reactivity in rats

Reactive oxygen species (ROS) such as superoxide anion (O2-*) and hydrogen peroxide (H2O2) can be produced by vascular endothelium and smooth muscle cells under diverse physiological and pathophysiological situations. These species are known to exert various deleterious effects by which they might induce changes in vascular reactivity. The aim of the present study was to evaluate the evolution of vascular susceptibility to H2O2 during aging in rats. Catalase activity was assessed in aortas from young adult (4 months) and aged (24 months) Wistar rats. In parallel experiments, isolated rings from both age groups were exposed to increasing doses of H2O2 (0, 0.1, 1, 5, or 10 mM) for 20 min and the residual vascular response to phenylephrine (PE = 10(-6) M) and acetylcholine (ACh = 10(-6) M) was evaluated. Our results indicate that aging increases aortic catalase activity (4 months: 0.20 +/- 0.02 IU/mg prot versus 24 months: 0.46 +/- 0.06 IU/mg prot, p < 0.001) while it exacerbates vascular sensitivity to H2O2. These results suggest that the observed increased H2O2-induced alterations of vascular reactivity during aging in rats might be due to increased sensitivity of the vasculature to ROS rather than to a decrease in the defense systems against these species.

Delayed oligodendrocyte degeneration induced by brief exposure to hydrogen peroxide

An in vitro model system of cultured oligodendrocytes was used to determine the susceptibility of these cells to oxidative stress induced by 15 min exposure to millimolar concentrations of hydrogen peroxide (H2O2). Following the exposure, the cells were incubated in normal growth medium, and analyzed at different time points. Although no cell loss was observed during the exposure period, there was a progressive depletion of adherent cells during the postexposure period as seen from either the number of recoverable nuclei, or from total RNA content of the cultures. Both the rate and the extent of cell deletion was directly dependent on H2O2 concentration. Cell death was preceded by structural alterations in the nuclear envelope resulting in "fragile" nuclei which disintegrated during isolation. Northern blot analysis showed that the expression of myelin-specific genes was rapidly downregulated in H2O2-treated cells. On the other hand, the expression of antiapoptotic gene, bcl-2 featured massive but transient upregulation. Oligodendrocyte degeneration also featured genomic DNA degradation into high molecular weight fragments, which are likely to represent cleaved chromosomal loops. The results demonstrate vulnerability of oligodendrocytes to oxidative stress that induces rapid degeneration and ultimately leads to delayed cell death. This feature is highly relevant to oligodendrocyte damage and depletion following ischemic, traumatic, or inflammatory insults to the central nervous system (CNS).

Antiarrhythmic effects of ceruloplasmin during reperfusion in the ischemic isolated rat heart

The ability of ceruloplasmin, an important serum antioxidant, to reduce the vulnerability of the isolated rat heart to reperfusion arrhythmias has been investigated. Bovine plasma ceruloplasmin was purified by chromatography on aminoethyl-agarose. Isolated rat hearts were submitted to 15 min of regional ischemia and 10 min of reperfusion. The dose-effect relationship and the role of ceruloplasmin conformational integrity in cardioprotection were established by treatment of ischemic hearts with ceruloplasmin at various concentrations (0.25, 0.5, 1, and 2 microM) and at different degrees of conformational integrity (A610/A280 = 0.02, 0.04, and 0.06), 5 min before reperfusion. Deferoxamine (20-500 microM) was used as a positive control. As negative controls we used chemically inactivated ceruloplasmin (1 microM), heat-denatured ceruloplasmin (1 microM), and albumin (1-4 microM). In the control group during the first 5 min of reperfusion, the incidence of total ventricular fibrillation was 100% and of irreversible ventricular fibrillation was 83%. The incidence of reversible and irreversible ventricular fibrillation was significantly decreased in the ceruloplasmin-treated groups in both a dose and molecular integrity dependent manner. Ceruloplasmin had no effect on the incidence of ventricular tachycardia. Deferoxamine reduced the incidence of ventricular fibrillation to the same degree as ceruloplasmin but at concentrations much higher than those of ceruloplasmin. Chemically inactivated ceruloplasmin, heat-denatured ceruloplasmin, and albumin had no protective effects on reperfusion-induced arrhythmias.

Does hydrogen peroxide exist "free" in biological systems?

Hydrogen peroxide (H2O2) can diffuse far from the site of production to intracellular locations where biological effects may be greater. The diffusion range is extended by H2O2 carriers formed spontaneously by hydrogen bonding with monomeric and polymeric compounds, including amino and dicarboxylic acids, peptides, proteins, nucleic acid bases, and nucleosides. Hydrogen peroxide adducts (HPAs) are readily synthesized, e.g., crystalline histidine (His)-H2O2 adducts. An equilibrium exists between an adduct-forming compound and H2O2. The detection and relative stabilities of HPAs are measured by the degree of decomposition of H2O2 as influenced by test compounds in buffered solution competing with glucose or fructose for H2O2. The HPAs delay decomposition of H2O2 up to several hundredfold. The overall charge on an HPA, i.e., its ability to penetrate cell membranes, influences the cytotoxic and clastogenic effects of H2O2. Growth inhibition of Salmonella typhimurium LT2 by H2O2 is enhanced by neutral HPAs but decreased by anionic HPAs. Addition of catalase 1, 10, or 30 min after inoculation of S. typhimurium LT2 reduces or nearly eliminates partial growth inhibition by H2O2, but a neutral HPA, especially His-H2O2, transported H2O2 into the cells within 1 min, and in about 10 min completely inhibited growth. The stability of HPAs decreases with increasing pH or increasing temperature, while added Fe(II) in the presence and absence of EDTA accelerates H2O2 and HPA decomposition. Calculations indicate H2O2 hydrogen bonds with nucleic acid-base pairs with no apparent bond strain and energy stabilization comparable to normal hydrogen bonding.

Oxygen metabolites induced by phorbol myristate acetate increase lateral diffusion of wheat germ agglutinin-labeled glycoconjugates in human polymorphonuclear leukocytes

To assess the general effects of protein kinase C (PKC) activation on cell membrane receptor mobility in human neutrophilic polymorphonuclear leukocytes (PMNLs), the lateral diffusion of fluoresceinated succinylated wheat germ agglutinin (S-WGA-FITC)-labeled membrane glycoconjugates was measured using fluorescence recovery after photobleaching (FRAP). Activation of PKC was achieved by incubating the PMNLs with different concentrations (5-100 nM) of phorbol myristate acetate (PMA). The membrane effects of dimethyl sulfoxide (DMSO), another possible membrane perturbant, were also studied. We found that PMA treatment (greater than or equal to 10 nM) increased the glycoconjugate diffusion coefficient (D) 2-2.5-fold. The mobile fraction (R) remained constant, around 30%. With DMSO, no effect on the diffusion was seen. The increase in lateral mobility due to cell stimulation with PMA was totally inhibited by catalase (200 units/ml) but only partly with superoxide dismutase (2000 units/ml). Exogenous hydrogen peroxide (0.01-5 mM) had no effect on glycoconjugate mobility in unstimulated cells. We therefore propose that activation of PKC mediates augmented mobility of glycoconjugate receptors in PMNL, a reaction that seems to be critically dependent on formation of reactive oxygen metabolites. The results indicate that endogenous formation of reactive metabolites upon receptor stimulation may have a general effect on receptor mobility.

Fenton reactions in lipid phases

Metal catalysis of membrane lipid oxidation has been thought to occur only at cell surfaces. However, conflicting observations of the pro-oxidant activity of ferric (Fe3+) vs ferrous (Fe2+) forms of various chelates have raised questions regarding this dogma. This paper suggests that the solubilities of iron complexes in lipid phases and the corresponding abilities to initiate lipid oxidation there, either directly or via Fenton-like production of reactive hydroxyl radicals, are critical determinants of initial catalytic effectiveness. Partitioning of Fe3+ and Fe2+ complexes and chelates into bulk phases of purified lipids was quantified by atomic absorption spectroscopy. mM solutions of iron salts partitioned into oleic acid at levels of about micromolar. Ethylenediamine tetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) chelates were somewhat less soluble, while adenosine diphosphate (ADP) chelates, and ferrioxamine were soluble as chelates at greater than 10(-5) M. Solubilities of all iron compounds in methyl linoleate were 10- to 100-fold lower. To determine whether Fenton-like reactions occur in lipid phases, H2O2 and either Fe2+ or Fe3+ and a reducing agent were partitioned into the lipid along with the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and free radical adducts were recorded by electron paramagnetic resonance (EPR). Hydroxyl radicals (OH.) adducts were observed in oleic acid, but in lipid esters secondary peroxyl radicals predominated, and the presence of OH. adducts was uncertain.

H2O2 as a DNA fragmenting agent in the alkaline elution interstrand crosslinking and DNA-protein crosslinking assays

A method for DNA fragmentation by H2O2 in the DNA alkaline elution procedure is described. Treatment of cell suspensions for 1 h with 100 microM H2O2 or 5 mM H2O2 at 0-1 degree C resulted in DNA breakage equivalent to doses of 300 and 3000 rad of gamma-rays, respectively. The elution profiles were reproducible and H2O2 was used for measurements of interstrand crosslinks and DNA-protein crosslinks induced in HeLa cells by mitomycin C, cis-diamminedichloroplatinum(II), and trans-diamminedichloroplatinum(II). The comparison of data obtained with the use of H2O2 and gamma-rays has shown that both methods have similar sensitivity and reproducibility.

Failure of desferrioxamine to modify the toxicity of paraquat in rats

The feasibility of using desferrioxamine (DF), an iron chelator, as a therapeutic agent against paraquat (PQ++) toxicity in male Sprague-Dawley rats was explored, based on the rationale of limiting toxic hydroxyl radical production from hydrogen peroxide by removing redox-active iron. Body weights, mortality, and lung histopathology were followed for periods up to 14 days after intraperitoneal injection of PQ++ (20 or 25 mg/kg body weight) with or without concurrent daily subcutaneous injections of DF (300 mg/day). Animals receiving PQ++ showed the expected typical patterns of mortality and of lung histopathology, namely: marked edema, subpleural hemorrhage, acute inflammation, perivascular mononuclear cell infiltrates, sloughing of alveolar and bronchiolar lining cells, and diffuse interstitial fibrosis. Desferrioxamine alone was non-toxic. Surprisingly, results when both PQ++ and DF were administered indicated a failure of DF to ameliorate toxic effects of PQ++ in the lung, and even suggested an accentuation of PQ++-induced damage by DF. Mortality data showed that PQ++/DF animals died in greater numbers (20 mg PQ++/kg) or died earlier (25 mg PQ++/kg) than animals receiving DF alone. Qualitative histopathology in PQ++/DF animals was comparable to PQ++ animals in early stages, but damage was more severe in both incidence and severity of lesions in PQ++/DF animals, particularly at the 25 mg PQ++/kg dose level. After 14 days, surviving animals receiving PQ++ alone showed almost complete resolution of previous inflammation and other acute effects, whereas in the only surviving PQ++/DF animal initial fibrosis had persisted and become more generalized. Thus, chelation therapy with DF may not be straightforward in its effects on PQ++ toxicity.