Comparing Students of Medical and Social Sciences in Terms of Self-Assessment of Perceived Stress, Quality of Life, and Personal Characteristics

The aim of this study was to compare medical and social sciences students’ outcomes in terms of self-perceived stress, quality of life, and personality traits. We put particular emphasis on external and internal differences in students of specific fields–medicine, nursing, psychology, and pedagogy. In a survey, 1,783 students from Medical University of Gdańsk and University of Gdańsk participated in our study, of whom 1,223 were included in the final statistical analysis. All of them were evaluated using valid and reliable questionnaires–TIPI-PL, PSS-10, and a one-item scale of quality of life. Stress turned out to have a negative effect on quality of life, regardless of the type of field of study. Moreover, students from different fields varied in terms of personality factors: conscientiousness, agreeableness, openness to experience, and emotional stability. In conclusion, many students regardless of their field suffer from high stress and report low quality of life, which potentially further affects their academic performance and social life.

Photodynamic Therapy in Dentistry

Photodynamic therapy (PDT), also known as photoradiation therapy, phototherapy, or photochemo-therapy, involves the use of a photoactive dye (photosensitizer) that is activated by exposure to light of a specific wavelength in the presence of oxygen. The transfer of energy from the activated photosensitizer to available oxygen results in the formation of toxic oxygen species, such as singlet oxygen and free radicals. These very reactive chemical species can damage proteins, lipids, nucleic acids, and other cellular components. Applications of PDT in dentistry are growing rapidly: the treatment of oral cancer, bacterial and fungal infection therapies, and the photodynamic diagnosis (PDD) of the malignant transformation of oral lesions. PDT has shown potential in the treatment of oral leukoplakia, oral lichen planus, and head and neck cancer. Photodynamic antimicrobial chemotherapy (PACT) has been efficacious in the treatment of bacterial, fungal, parasitic, and viral infections. The absence of genotoxic and mutagenic effects of PDT is an important factor for long-term safety during treatment. PDT also represents a novel therapeutic approach in the management of oral biofilms. Disruption of plaque structure has important consequences for homeostasis within the biofilm. Studies are now leading toward selective photosensitizers, since killing the entire flora leaves patients open to opportunistic infections. Dentists deal with oral infections on a regular basis. The oral cavity is especially suitable for PACT, because it is relatively accessible to illumination.

Cationic porphyrin-mediated photodynamic inactivation of Candida biofilms and the effect of miconazole

The formation of biofilms by Candida and the increasing resistance of Candida species to antifungals contribute to the high recurrence rates of denture stomatitis. This increase has stimulated an interest in antimicrobial photodynamic therapy (aPDT) as an alternative treatment. We examined the photoactivity of the porphyrin-based photosensitizer, TMP-1363, against biofilms of C. albicans, C. glabrata, C. tropicalis and C. parapsilosis, and the effect of the combined use of miconazole and aPDT. Biofilms of three American Type Culture Collection (ATCC) strains and four clinical isolates developed on poly(methyl methacrylate) (PMMA) disks, were incubated with miconazole, followed by treatment with TMP-1363 for 30 min at 37°C. The plates were exposed to broadband visible light at a distance of 10 cm to the plate, for 30 min (irradiance at the surface of the plate: 32.5 mW/cm2). The metabolic activity of the biofilms was measured by the XTT assay. ATCC strains and C. glabrata 7531/06 were not sensitive to TMP-aPDT, whereas the metabolic activities of the remaining three clinical isolates were reduced to 64.2 ± 5.5% of controls. Miconazole at 25 μg/ml decreased the viability of all strains except the ATTCC strain C. albicans MYA274; however its combination with aPDT was effective against this strain, suggesting a synergistic interaction. Effects of miconazole and aPDT on C. albicans MYA 2732, C. albicans 6122/06 were additive. With C. tropicalis and C. parapsilosis, the combined treatment had a higher, but not entirely additive, cytotoxic effect. The combined use of miconazole and TMP-aPDT is advantageous in the treatment of biofilms of a number of Candida species and strains, but not all. The molecular basis of this differential response is not known.

Anionic Liposomes Inhibit Human Immunodeficiency Virus Type 1 (HIV-1) Infectivity in CD4+ A3.01 and H9 Cells

Immunodeficiency viruses undergo fusion with liposomes containing anionic phospholipids (Larsen etal., 1990). We have investigated the effect of liposomes composed of cardiolipin, phosphatidylserine or phosphatidylinositol, on the infectivity of three strains of HIV-1 in A3.01 and H9 cells, measured by p24 (gag) production in the medium. The infectivity of HIV-1 in A3.01 or H9 cells was inhibited by the presence of cardiolipin liposomes during a 2 h infection period, with IC50's of 23.0, 4.8, and 5.0 μM phospholipid, respectively, for the different strains. Liposomes composed of phosphatidylserine or phosphatidylinositol were ineffective under similar conditions. However, prolonged pre-incubation of the virus with these liposomes also inhibited infectivity. Inhibition of virus binding to cells could not account for the inhibition of infectivity. We propose that the fusion products of HIV-1 and anionic liposomes are impaired in their ability to fuse with the plasma membrane.

Miconazole activity against Candida biofilms developed on acrylic discs

Oral candidiasis in the form of Candida-associated denture stomatitis (CaDS) is associated with Candida adhesion and biofilm formation on the fitting surface of poly (methyl methacrylate) (PMMA) dentures. Candida biofilms show considerable resistance to most conventional antifungal agents, a phenomenon that is considered a developmental-phase-specific event that may help explain the high recurrence rates associated with CaDS. The aim of this study was to examine the activity of miconazole towards in vitro-grown mature Candida biofilms formed on heat-cured PMMA discs as a standardized model. The effect of miconazole nitrate on Candida biofilms developed on acrylic discs was determined for C. albicans MYA-2732 (ATCC), C. glabrata MYA-275 (ATCC), and clinical isolates, C. albicans 6122/06, C. glabrata 7531/06, C. tropicalis 8122/06, and C. parapsilosis 11375/07. Candida biofilms were developed on heat-cured poly(methyl methacrylate) discs and treated with miconazole (0.5 - 96 μg/ml). The metabolic activity of the biofilms was measured by the XTT reduction assay. The minimum inhibitory concentrations (MICs) of miconazole against Candida species were determined by the microdilution method. The MICs for miconazole for the investigated strains ranged from 0.016-32 μg/ml. Treatment with miconazole resulted in a significant reduction of biofilm metabolic activity for all strains. The highest inhibition was observed at 96 μg/ml miconazole. In the case of C. glabrata MYA-275 and C. tropicalis 8122/06 this corresponded to 83.7% and 75.4% inhibition, respectively. The lowest reduction was observed for C. parapsilosis 11375/07-46.1%. For all Candida strains there was a strong correlation between MIC values and miconazole concentrations corresponding to a reduction of metabolic activity of the biofilm by 50%. Miconazole exhibits high antifungal activity against Candida biofilms developed on the surface of PMMA discs. The study provides support for the use of miconazole as an effective agent for the treatment of CaDS.

Metal particles in a ceramic matrix�?�scanning electron microscopy and transmission electron microscopy characterization

This paper is concerned with ceramic matrix (Al(2)O(3)) composites with introduced metal particles (Ni, Fe). The composites were obtained via sintering of powders under very high pressure (2.5 GPa). Scanning electron microscopy and transmission electron microscopy were chosen as the tools for the identification and description of the shape, size and distribution of the metal particles. The Al(2)O(3)-Ni composite contained agglomerates of the Ni particles surrounded by ceramic grains and nanometre-size Ni particles located inside the ceramic grains and at the ceramic grain boundaries. In the Al(2)O(3)-Fe composite, the Fe particles were mostly surrounded by ceramic grains. Moreover, holes left by the Fe particles were found. The high pressure used in the fabrication of the composites changed the shape of the metal and ceramic powder grains via plastic deformation.

Influence of antifungal polyenes on the adhesion of Candida albicans and Candida glabrata to human epithelial cells in vitro

Candidal adherence to mucosal surfaces is considered as the first step in the pathogenesis of oral candidiasis. We examined the effect of antifungal polyenes, amphotericin B, nystatin and natamycin, at sublethal and minimum inhibitory concentrations (MICs) on the adherence of Candida albicans and Candida glabrata to HeLa cervical carcinoma and HSC-3 oral squamous cell carcinoma cells. A total of six oral Candida isolates were used throughout the study. Two Candida strains, C. albicans (44990) and C. glabrata (MYA-275) were obtained from ATCC. Four Candida strains, C. albicans 19 and 24 and C. glabrata 15 and 21, were isolated from patients with documented Candida-associated denture stomatitis. Cells were either incubated with Candida in the presence of the drug, or pre-incubated with yeasts and exposed subsequently to the drug. In the drug-free controls, the mean number of C. albicans yeasts associated with HeLa cells obtained from all experiments (130.1+/-10.1 yeasts/mm(2)) was significantly greater than that for HSC-3 cells (114.7+/-10.1 yeasts/mm(2); P<0.025). For C. glabrata, the mean adherence to HeLa and HSC-3 cells was 84.4+/-5.5 and 84.4+/-3.3 yeasts/mm(2), respectively, and these values were not statistically different (P>0.4). Candidal adherence was significantly reduced when the tested polyenes were present during the "adherence phase". The obtained values were significantly different from the controls, except for the effect of nystatin at the MIC on the adherence of C. glabrata strain MYA-275 to HeLa cells (P<0.375). Amphotericin B had the highest effect against both Candida species, reducing adherence by approximately 50 and approximately 60%, at the MIC and sublethal concentrations, respectively. The susceptibility of cell-associated Candida to polyenes was decreased markedly and the treatment did not result in significant detachment of adherent yeasts. The reduction in adherence was between 2 and 10%, when compared to the drug-free controls. These findings suggest that sub-therapeutic levels of polyenes that are likely to persist in the oral cavity following topical treatment may modulate candidal colonization when present during the "adherence phase".

Delivery of novel macromolecular drugs against HIV-1

The development of new low molecular weight drugs against human immunodeficiency virus Type 1 (HIV-1) targets other than reverse transcriptase (RT) and protease, such as the integrase and the envelope glycoprotein, is likely to take many years. Macromolecular drugs, including antisense oligonucleotides, ribozymes, RNA decoys and transdominant mutant proteins, may be able to interfere with a relatively large number of viral targets, thereby decreasing the likelihood of the emergence of drug-resistant strains. It may also be relatively easy to alter the sequence of some of the macromolecular drugs to counter emerging drug-resistant viruses. The delivery of antisense oligonucleotides and ribozymes to HIV-1 infected or potentially infectable cells by antibody-targeted liposomes, certain cationic lipid formulations and pH-sensitive liposomes results in significant anti-HIV-1 activity. These carriers not only facilitate cytoplasmic delivery but also protect the drugs from nuclease digestion. Delivery of therapeutic genes (another form of macromolecular drug) to target cells is an important challenge of gene therapy. Following delivery by a viral vector, sufficient levels of gene expression must be maintained over an extended period of time to have therapeutic activity. Robust expression of therapeutically useful ribozymes, antisense, decoys and aptamers can be achieved by the use of Pol III expression systems. Moloney murine leukaemia virus- (MoMuLV), adeno-associated virus (AAV)-, or HIV-derived vectors expressing a variety of therapeutic genes have been used successfully to inhibit HIV-1 replication in cultured cells.

Rev-binding aptamer and CMV promoter act as decoys to inhibit HIV replication

We examined whether the antiviral effect of an HIV-1 Rev-binding aptamer [RBE(apt)] could be enhanced by a ribozyme directed against the HIV-1 env gene, and whether the antiviral activity was affected by different promoters. The efficacy of the aptamer and ribozyme DNAs was tested in HeLa cells co-transfected with the HIV-1 proviral clones, HXBDeltaBgl or pNL4-3, using transferrin-lipoplexes. The RBE(apt) and anti-env ribozyme genes were inserted into the pTZU6+27 plasmid, or constructed under the control of the human cytomegalovirus (CMV) or Rous sarcoma virus (RSV) promoters. The parental vector plasmids were used as controls. Co-transfection of the pTZU6+27 RBE(apt) plasmid with HXBDeltaBgl, or pNL4-3, at a weight ratio of 5:1, inhibited p24 production by 70 and 45%, respectively. The RSV RBE(apt) plasmid co-transfected with either HIV clone, at the same weight ratio, reduced viral production by 88%. The addition of the anti-env ribozyme to the RSV RBE(apt) did not enhance its antiviral activity. When the constructs were under the control of the CMV promoter, the expression of the HIV plasmids was very low and was independent of the presence of the RBE(apt). Thus, the effect of the RBE(apt) was strongly dependent on the promoter of the tested construct. The anti-HIV activity of the CMV RBE(apt) construct was non-specific, because co-transfection with either pCMV. SPORT-betagal or pCMVlacZ significantly suppressed HIV production from the HIV proviral clones. The reduction in p24 could not be attributed to the non-specific toxicity of the transfection procedure. Transfection of acutely HIV-infected HeLa-CD4 cells with pCMV.SPORT-betagal reduced the p24 level by 35%, while the expression of the U6 RBE(apt) did not affect p24 production. The suppression of HIV production from the HIV proviral clones by the CMV promoter constructs in the co-transfection assays may be explained by competition for transcription factors (TFs) between HIV and CMV promoters. This observation points to the potential for misleading results in co-transfections involving CMV constructs and HIV.

Secretory leukocyte protease inhibitor (SLPI): oxidation of SLPI does not explain its variable anti-HIV activity

Secretory leukocyte protease inhibitor (SLPI) has been proposed as a potential inhibitor of HIV-1 infection in human saliva. Although the ability of recombinant (r) SLPI to inhibit HIV-1 infection of macrophages and primary T-cells has been demonstrated by two independent laboratories, evidence to the contrary has also been reported. This study re-examines the anti-HIV effect of rSLPI and investigates the effects of repeated freeze-thawing and oxidation on the anti-HIV activity of rSLPI. rSLPI inhibited HIV-1BaL infection of human macrophages in a highly variable manner. HPLC and electrospray ionization mass spectrometry (ESI) analyses indicated that variability in our inhibition data could not be attributed to the degradation or oxidation of rSLPI. These results suggest that the variable anti-HIV effect of rSLPI may be due to differential expression of the cell-surface molecule(s) to which SLPI binds rather than to changes in the rSLPI molecule.

Anti-HIV activity of amphotericin B-cholesteryl sulfate colloidal dispersion in vitro

We examined whether the anti-HIV-1 activity of the polyene antibiotic Amphotericin B (AMB) is retained following incorporation into sterically stabilized 'Stealth' liposomes (L-AMB) with prolonged circulation in vivo, or cholesteryl sulfate colloidal dispersions (CD-AMB). The effects of the different preparations on acute infection of H9 cells with HIV-1IIIB, spreading of the virus from chronically infected H9/HTLV-IIIB cells to SupT1 cells, and HIV-1-induced syncytium formation were evaluated. Infection was monitored by p24 levels in culture supernatants. L-AMB did not affect HIV-1 infection. When present only during initial infection, AMB (3-20 microg/ml) reduced p24 levels by 70-80% after 7 and 10 days post-infection, while CD-AMB inhibited p24 production by approximately 30-40% at day 7 and 50-60% at day 10. The inhibitory effect of CD-AMB and AMB was enhanced by continuous treatment of acutely infected cells. The reduction of p24 production during continuous treatment was not due to cytotoxicity. During spreading of infection from infected to uninfected cells, AMB almost completely inhibited virus production while CD-AMB reduced both p24 production and the cytopathic effect in a dose-dependent manner. HIV-1 induced syncytium formation was slightly inhibited by AMB but not by CD-AMB. Because CD-AMB is considerably less cytotoxic than AMB, its ability to inhibit HIV infection in vivo needs to be evaluated further.

Liposome-mediated delivery of antiviral agents to human immunodeficiency virus-infected cells

Intracellular delivery of novel macromolecular drugs against human immunodeficiency virus type-1 (HIV-1), including antisense oligodeoxynucleotides, ribozymes and therapeutic genes, may be achieved by encapsulation in or association with certain types of liposomes. Liposomes may also protect these drugs against nucleases. Low-molecular-weight, charged antiviral drugs may also be delivered more efficiently via liposomes. Liposomes were targeted to HIV-1-infected cells via covalently coupled soluble CD4. An HIV-1 protease inhibitor encapsulated in conventional negatively charged multilamellar liposomes was about 10-fold more effective and had a lower EC90 than the free drug in inhibiting HIV-1 production in human monocyte-derived macrophages. The drug encapsulated in sterically stabilized liposomes was as effective as the free drug. The EC50 of the reverse transcriptase inhibitor 9-(2-phosphonylmethoxyethyl)adenine (PMEA) was reduced by an order of magnitude when delivered to HIV-1-infected macrophages in pH-sensitive liposomes. A 15-mer antisense oligodeoxynucleotide against the Rev response element was ineffective in free form against HIV-1 replication in macrophages, while delivery of the oligonucleotide in pH-sensitive liposomes inhibited virus replication. The oligodeoxynucleotide encapsulated in sterically stabilized pH-sensitive liposomes with prolonged circulation in vivo, which were recently developed in the laboratories of the authors, was also highly effective. A ribozyme complementary to HIV-1 5'-LTR delivered in pH-sensitive liposomes inhibited virus production by 90%, while the free ribozyme caused only a slight inhibition. Cationic liposome-mediated co-transfection of the HIV-regulated diphtheria toxin A fragment gene and a proviral HIV clone into HeLa cells completely inhibited virus production, while the frame-shifted mutant gene was ineffective. Co-transfection of the proviral genome and a gene encoding a Rev-binding aptamer into HeLa cells via transferrin-associated cationic liposomes inhibited virus production. These studies indicate that liposomes can be used to facilitate the intracellular delivery of certain anti-HIV agents and to enhance their therapeutic effects. These properties may be particularly advantageous in the development of novel macromolecular drugs, which may be necessary because of the emergence of virus strains resistant to the currently available drugs.

Receptor ligand-facilitated cationic liposome delivery of anti-HIV-1 Rev-binding aptamer and ribozyme DNAs

We examined whether HIV-1 gene expression could be inhibited by the anti-HIV Rev-binding aptamer [RBE(apt)], and whether the antiviral effect of the aptamer could be enhanced by a ribozyme directed against the HIV-1 env gene. Since cationic liposomes are relatively safe and non-immunogenic for in vivo gene delivery, we tested the effectiveness of the aptamer and ribozyme DNAs in HeLa cells, using Lipofectin reagent in a transient transfection assay. To increase the transfection efficiency, lipofectin was mixed with transferrin before subsequent addition of DNA. Co-transfection of HeLa cells with the RBE(apt) and the proviral HIV clone, HXBdeltaBgl, resulted in inhibition of virus production. Specific inhibition of viral p24 production following co-transfection of the RBE(apt) and HIV proviral DNAs was observed. These data provide strong support for the use of in vitro evolved ligands as potential anti-HIV agents. The addition of the anti-env ribozyme to the aptamer construct did not further enhance the antiviral activity, suggesting either that we had reached the limits of inhibition in this assay, or that the ribozyme was not able to access its target site with Rev bound to the RBE aptamer. The observed inhibition of p24 production could not be attributed to the non-specific toxicity of the transfection procedure, because no difference in viability was observed between the RBE(apt)- and the vector control-treated cells. All of the aptamer-ribozyme constructs as well as the RBE(apt) were similarly effective.

Delivery of an anti-HIV-1 ribozyme into HIV-infected cells via cationic liposomes

Cationic liposome-mediated intracellular delivery of a fluorescein-labeled chimeric DNA-RNA ribozyme targeted to the HIV-1 5' LTR was investigated, using THP-1, THP-1/HIV-1IIIB or HeLa/LAV cells. Different fluorescence patterns were observed when the cells were exposed to Lipofectamine, Lipofectin or DMRIE:DOPE (1:1) complexed to the ribozyme. With Lipofectamine intense cell-associated fluorescence was found. Incubation with Lipofectin resulted in less intense diffuse fluorescence, while with DMRIE an intense but sporadic fluorescence was observed. Differentiated THP-1/HIV-1IIIB cells were more susceptible to killing by liposome-ribozyme complexes than THP-1 cells. Under non-cytotoxic conditions (a 4-h treatment) complexes of 5, 10 or 15 microM Lipofectin or DOTAP:DOPE (1:1) and ribozyme, at lipid:ribozyme ratios of 8:1 or 4:1, did not affect p24 production in THP-1/HIV-1IIIB cells in spite of the intracellular accumulation of the ribozyme. A 24-h exposure of THP-1/HIV-1IIIB cells to 5 microM Lipofectin or DOTAP:DOPE (1:1) complexed with either the functional or a modified control ribozyme reduced virus production by approximately 30%. Thus, the antiviral effect of the liposome-complexed ribozyme was not sequence-specific. In contrast, the free ribozyme at a relatively high concentration inhibited virus production by 30%, while the control ribozyme was ineffective, indicating a sequence-specific effect. Both Lipofectin and DOTAP complexed with ribozyme were toxic at 10 and 15 microM after a 24-h treatment. A 4-h treatment of HeLa/LAV cells with Lipofectin at 5, 10 or 15 microM was not toxic to the cells, but also did not inhibit p24 production. In contrast, treatment of HeLa CD4+ cells immediately after infection with HIV-1IIIB at the same lipid concentrations and lipid:ribozyme ratios was cytotoxic. Our results indicate that the delivery of functional ribozyme into cells by cationic liposomes is an inefficient process and needs extensive improvement before it can be used in ex vivo and in vivo applications.

Platelet-activating factor mediates angiotensin II-induced proteinuria in isolated perfused rat kidney

Isolated kidney preparations (IPK) from male Sprague Dawley rats perfused at constant pressure were used to evaluate the effect of angiotensin II (AII) and platelet-activating factor (PAF) on renal function and urinary protein excretion. Compared with basal, intrarenal infusion of AII at 8 ng/min caused a progressive increase in protein excretion (11 +/- 6 versus 73 +/- 21 micrograms/min) in parallel with a decline in renal perfusate flow (RPF) (29 +/- 3 versus 18 +/- 3 ml/min). Addition to the perfusate of PAF at 50 nM final concentration also induced proteinuria (9 +/- 4 versus 55 +/- 14 micrograms/min) but did not change RPF (29 +/- 3 versus 30 +/- 3 ml/min). Preexposure of isolated kidneys to the PAF receptor antagonist WEB 2086 prevented the increase in urinary protein excretion induced by AII infusion (basal: 13 +/- 6; post-AII: 12 +/- 7 micrograms/min) but failed to prevent the vasoactive effect of AII (RPF, basal: 30 +/- 2; post-AII: 21 +/- 3 ml/min). In additional experiments, dexamethasone reduced the proteinuric effect of PAF remarkably. These results indicate that in isolated kidney preparation: (1) AII infusion induced proteinuria and decreased RPF; and (2) the effect of AII in enhancing urinary protein excretion was completely prevented by a specific PAF receptor antagonist, which, however, did not influence the AII-induced fall in RPF. It is suggested that PAF plays a major role in AII-induced changes in the permselective function of the glomerular capillary barrier.

Cationic liposome-mediated expression of HIV-regulated luciferase and diphtheria toxin a genes in HeLa cells infected with or expressing HIV

HIV-regulated expression of the diphtheria toxin A fragment gene (HIV-DT-A) is a potential gene therapy approach to AIDS. Since cationic liposomes are safe and non-immunogenic for in vivo gene delivery, we examined whether LipofectAMINE or DMRIE reagent could mediate the transfection of HIV-DT-A (pTHA43) or the HIV-regulated luciferase gene (pLUCA43) into HIV-infected or uninfected HeLa cells. pLUCA43 was expressed at a 10(3)-fold higher level in HeLa/LAV cells than in uninfected HeLa cells, while the extent of expression of RSV-regulated luciferase was the same in both cell lines. Co-transfection of HeLa cells with pTHA43 and the proviral HIV clone, HXB deltaBgl, resulted in complete inhibition of virus production. In contrast, the delivery of HIV-DT-A to chronically infected HeLa/LAV or HeLa/IIIB cells, or to HeLa CD4+ cells before infection, did not have a specific effect on virus production, since treatment of cells with control plasmids also reduced virus production. This reduction could be ascribed to cytotoxicity of the reagents. The efficiency of transfection, as measured by the percentage of cells expressing beta-gal, was approximately 5%. Thus, cationic liposome-mediated transfection was too inefficient to inhibit virus production when the DT-A was delivered by cationic liposomes to chronically- or de novo- infected cells. However, when both the virus and DT-A genes were delivered into the same cells by cationic liposomes, DT-A was very effective at inhibiting virus production. Our results indicate that the successful use of cationic liposomes for gene therapy will require the improvement of their transfection efficiency.

The anti-HIV-1 activity associated with saliva

This review summarizes the data on the anti-human immunodeficiency virus (HIV) activity associated with saliva and the possible routes of oral transmission of HIV. Saliva can be passed from an HIV-infected individual to an uninfected person via sexual or non-sexual activities. The relative risk of HIV transmission through saliva is a subject of continuing concern for dental practitioners. HIV-infected individuals frequently have oral lesions that can cause bleeding and release of the virus into the oral cavity. In addition, viral p24 and HIV-1 RNA were detected in tonsils and adenoids even in asymptomatic seropositive individuals. Nevertheless, the potential HIV-infectivity of saliva is low, although both infectious HIV-1 and HIV DNA have been detected in saliva. This observation has led to the suggestion that saliva may contain factors that inhibit HIV-1 infectivity. At least two anti-HIV activities have been partially characterized: (i) physical entrapment of HIV by high-molecular-weight molecules (e.g., mucins), and (ii) inhibition of viral infection by soluble proteins. Several studies have indicated that, of the salivary proteins evaluated, recombinant secretory leukocyte protease inhibitor (rSLPI) could inhibit HIV-1 infection in macrophages at physiological concentrations. The anti-HIV activity of the serine protease inhibitor rSLPI is most likely due to its interaction with a cell-surface molecule(s) other than the primary HIV-1 receptor, CD4, and may involve (i) inhibition of cell-surface serine protease(s), and/or (ii) interaction with other human-specific co-factors essential for viral entry.

Human immunodeficiency virus type-1 (HIV-1) infection increases the sensitivity of macrophages and THP-1 cells to cytotoxicity by cationic liposomes

Cationic liposomes may be valuable for the delivery of anti-sense oligonucleotides, ribozymes, and therapeutic genes into human immunodeficiency virus type 1 (HIV-1)-infected and uninfected cells. We evaluated the toxicity of three cationic liposomal preparations, Lipofectamine, Lipofectin, and 1, 2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide (DMRIE) reagent, to HIV-infected and uninfected cells. Monocyte/macrophages were infected with HIV-1BaL and treated with liposomes in medium containing 20% fetal bovine serum (FBS) for 4 h or 24 h at 37 degree C. Uninfected monocytic THP-1 cells and chronically infected THP-1/HIV-1IIIB cells were treated with phorbol 12-myristate 13-acetate (PMA) and exposed to liposomes in the presence of 10% FBS. Toxicity was evaluated by the Alamar Blue assay and viral p24 production. The toxic effect of cationic liposomes was very limited with uninfected cells, although concentrations of liposomes that were not toxic within a few days of treatment could cause toxicity at later times. In HIV-1BaL-infected macrophages, Lipofectamine (up to 8 microM) and Lipofectin (up to 40 microM) were not toxic after a 4-h treatment, while DMRIE reagent at 40 microM was toxic. While a 4-h treatment of THP-1/HIV-1IIIB cells with the cationic liposomes was not toxic, even up to 14 days post-treatment, all three cationic liposomes were toxic to cells at the highest concentration tested after a 24-h treatment. Similar results were obtained with the Alamar Blue assay, Trypan Blue exclusion and a method that enumerates nuclei. Infected cells with relatively high overall viability could be impaired in their ability to produce virions, indicating that virus production appears to be more sensitive to treatment with the cationic liposomes than cell viability. Our results indicate that HIV-infected cells are more susceptible than uninfected cells to killing by cationic liposomes. The molecular basis of this differential effect is unknown; it is proposed that alterations in cellular membranes during virus budding cause enhanced interactions between cationic liposomes and cellular membranes.

The stoichiometry of the cytochrome P-450-catalyzed metabolism of methoxyflurane and benzphetamine in the presence and absence of cytochrome b5

The complete stoichiometry of the metabolism of the cytochrome b5 (cyt b5)-requiring substrate, methoxyflurane, by purified cytochrome P-450 2B4 was compared to that of another substrate, benzphetamine, which does not require cyt b5 for its metabolism. Cyt b5 invariably improved the efficiency of product formation. That is, in the presence of cyt b5 a greater percentage of the reducing equivalents from NADPH were utilized to generate substrate metabolites, primarily at the expense of the side product, superoxide. With methoxyflurane, cyt b5 addition always resulted in an increased rate of product formation, while with benzphetamine the rate of product formation remained unchanged, increased or decreased. The apparently contradictory observations of increased reaction efficiency but decrease in total product formation for benzphetamine can be explained by a second effect of cyt b5. Under some experimental conditions cyt b5 inhibits total NADPH consumption. Whether stimulation, inhibition, or no change in product formation is observed in the presence of cyt b5 depends on the net effect of the stimulatory and inhibitory effects of cyt b5. When total NADPH consumption is inhibited by cyt b5, the rapidly metabolized, highly coupled (approximately equal to 50%) substrate, benzphetamine, undergoes a net decrease in metabolism not counterbalanced by the increase in the efficiency (2-20%) of the reaction. In contrast, in the presence of the slowly metabolized, poorly coupled (approximately equal to 0.5-3%) substrate, methoxyflurane, inhibition of total NADPH consumption by cyt b5 was never sufficient to overcome the stimulation of product formation due to an increase in efficiency of the reaction.

Differential effects of a hydrophobic tripeptide on human immunodeficiency virus type 1 (HIV-1)-induced syncytium formation and viral infectivity

The synthetic hydrophobic peptide, Z-D-Phe-L-Phe-Gly, was shown previously to inhibit the infectivity of paramyxoviruses and the fusion of Sendai virus with liposomes. We examined the ability of this peptide to inhibit HIV-1 infectivity in A3.01, Sup-T1, and H9 cells and syncytium formation between these cells and chronically infected H9 cells. Although the peptide inhibited syncytium formation in a dose-dependent manner, its effect on virus infectivity was very limited. Our results suggest that the mechanisms of interaction of the HIV-1 envelope glycoprotein gp120/gp41 with the target cell membrane leading to membrane fusion may be different in cell-cell and virus-cell fusion.

A monoclonal antibody to the gp120-CD4 complex has differential effect on HIV-induced syncytium formation and viral infectivity

A murine monoclonal antibody (MAb F-91-55) raised against the complex of soluble CD4 and human immunodeficiency virus type 1 (HIV-1) gp120 had previously been found to inhibit syncytium formation without inhibiting the interaction of CD4 with gp120, and its binding site was localized within the first two domains (D1/D2) of CD4. We investigated whether this antibody inhibited the infectivity of HIV-1 in the CD4+ T cell lines A3.01, Sup-T1 and H9. We also examined the effect of the antibody on syncytium formation between these cells and chronically infected H9 cells. Syncytium formation was found to depend critically on the incubation medium used. The effect of the MAb on HIV-1 infectivity was very limited with A3.01 and Sup-T1 cells, although it inhibited syncytium formation between A3.01 or Sup-T1 and chronically infected H9 cells. In contrast, the MAb inhibited significantly the infectivity of HIV-1 in H9 cells, but it also inhibited syncytium formation between H9 and chronically infected H9 cells to a greater extent than in the case of the other cell lines. Our results indicate that cellular systems used for syncytium assays differ in their susceptibility to inhibitory antibodies. In the A3.01 and Sup-T1 cell systems, the differences in the ability of the MAb to block viral entry or syncytium formation raise the possibility that the mechanisms of interaction of gp120/gp41 with cell membrane CD4 may be different in cell-cell and virus-cell membrane fusion.

Liposome targeting to human immunodeficiency virus type 1-infected cells via recombinant soluble CD4 and CD4 immunoadhesin (CD4-IgG)

HIV-infected cells producing virions express the viral envelope glycoprotein gp120/gp41 on their surface. We examined whether liposomes coupled to recombinant soluble CD4 (sCD4, the ectodomain of CD4 which binds gp120 with high affinity) could specifically bind to HIV-infected cells. sCD4 was chemically coupled by 2 different methods to liposomes containing rhodamine-phosphatidylethanolamine in their membrane as a fluorescent marker. In one method, sCD4 was thiolated with N-succinimidyl acetylthioacetate (SATA) and coupled to liposomes via a maleimide-derivatised phospholipid. In the other method, the oligosaccharides on sCD4 were coupled to a sulfhydryl-derivatised phospholipid, utilizing the bifunctional reagent, 4-(4-N-maleimidophenyl)butyric acid hydrazide (MPBH). The association of the liposomes with HIV-1-infected or uninfected cells was examined by flow cytometry. CD4-coupled liposomes associated specifically to chronically infected H9/HTLV-IIIB cells, but not to uninfected H9 cells. CD4-coupled liposomes also associated specifically with monocytic THP-1 cells chronically infected with HIV-1 (THP-1/HIV-1IIIB). Control liposomes without coupled CD4 did not associate significantly with any of the cells, while free sCD4 could competitively inhibit the association of the CD4-coupled liposomes with the infected cells. The chimeric molecule CD4-immunoadhesin (CD4-IgG) could also be used as a ligand to target liposomes with covalently coupled Protein A (which binds the Fc region of the CD4-IgG) to H9/HTLV-IIIB cells. The CD4-liposomes inhibited the infectivity of HIV-1 in A3.01 cells, and also bound rgp120. Our results suggest that liposomes containing antiviral or cytotoxic agents may be targeted specifically to HIV-infected cells.

Long-term noncytopathic productive infection of the human monocytic leukemia cell line THP-1 by human immunodeficiency virus type 1 (HIV-1IIIB)

A long-term, noncytopathic, productive infection of the monocytic leukemia cell line THP-1 with human immunodeficiency virus type 1 (HIV-1IIIB) was established. Both infected cells (THP-1/HIV-1IIIB) growing in suspension and uninfected, phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells, which are adherent, showed ultrastructural characteristics of differentiated cells. PMA-treated THP-1 cells could not be productively infected with HIV-1IIIB. THP-1/HIV-1IIIB cells produced virions mainly by budding at the plasma membrane. These cells retained the ability to differentiate into macrophage-like cells, capable of releasing the virus for extended periods of time (e.g., 40 days). PMA-mediated differentiation of THP-1/HIV-1IIIB cells modified the pattern of virus localization. Immediately after PMA treatment mature viral particles were primarily observed extracellularly. After 21 days in culture, however, the virions accumulated in intracellular vacuoles. THP-1/HIV-1IIIB cells may be used as a useful model system for HIV-infected macrophages.

Enhancement of human immunodeficiency virus type 1 infection by cationic liposomes: the role of CD4, serum and liposome-cell interactions

We have reported previously the enhancement of the infectivity of human immunodeficiency virus type 1 (HIV-1) by liposomes composed of the cationic lipid N-[2,3-(dioleyloxy) propyl]-N,N,N-trimethylammonium chloride (DOTMA). To determine the mechanism by which this process occurs, we have investigated the role of CD4, serum concentration and liposome-cell interactions in the DOTMA-mediated stimulation of HIV-1 infection of A3.01 cells. Serum alone significantly inhibited the binding and infectivity of HIV-1, but DOTMA-mediated enhancement of infectivity was more pronounced in the presence of serum than in its absence. HIV-1 binding to cells was increased in the presence of DOTMA liposomes, DEAE-dextran and polybrene, all of which also enhanced infectivity to a similar extent at comparable concentrations. Fluorescence dequenching measurements indicated that DOTMA liposomes fused with HIV-1, but not with cell membranes, in the presence of serum. The enhancing effect of DOTMA liposomes on HIV-1 infectivity was CD4-dependent, and appeared to involve virus-liposome fusion and liposome binding to the cell surface. DOTMA liposomes did not mediate infection of the CD4-K562 and Raji cell lines.

Liposomes modulate human immunodeficiency virus infectivity

We have investigated the effects of the fusion of liposomes with human immunodeficiency virus type 1 (HIV-1LVA) on the ability of the virus to infect CD4+ and CD4- cells. Fluorescence dequenching measurements indicated that HIV-1 fuses with liposomes composed of either cardiolipin (CL) or N-[2,3-(dioleyloxy) propyl]-N,N,N-trimethyl ammonium chloride (DOTMA) but not appreciably with dioleoylphosphatidylcholine (DOPC) liposomes. Pre-incubation of HIV-1 with DOTMA liposomes enhanced virus production (measured by p24 gag antigen production in the culture medium and in situ) in CD4+ A3.01 and H9 cells in a concentration-dependent manner, but did not mediate the infection of the CD4- cell line, K562. Preincubation of HIV-1 with between 10 and 30 microM-DOTMA liposomes, and subsequent incubation with A3.01 cells, resulted in the production of about 30-fold greater levels of virus than controls. The presence of DOTMA liposomes during the incubation of A3.01 cells with HIV-1 enhanced the infectivity of the virus up to 90-fold compared to controls. Conversely, preincubation of HIV-1 with CL liposomes inhibited infection of A3.01 cells, dependent on the concentration of liposomes; DOPC liposomes did not alter the infectivity of the virus under any of the incubation conditions. Our results thus indicate that fusion of HIV-1 with liposomes alters the ability of the virus to infect its target cells.

Ethanol-inducible cytochrome P450 in rabbits metabolizes enflurane

Following anaesthesia with enflurane, some patients receiving isoniazid have increased serum concentrations of fluoride ion, presumably because of induction of an isozyme of cytochrome P450 which is responsible for enflurane biodegradation. In rats, isoniazid and ethanol enhance metabolism of enflurane and also induce a form of cytochrome P450 which is homologous with a form of rabbit liver cytochrome P450 known as 3a. Isoniazid, ethanol and imidazole increase the concentration of cytochrome P450 3a in hepatic microsomes. We have pretreated rabbits with imidazole, the most potent of the three inducers of isozyme 3a, to determine if the hepatic microsomal metabolism of enflurane is enhanced and if purified isozyme 3a catalyses the oxidation of enflurane. Imidazole produced a 250% increase in the hepatic microsomal metabolism of enflurane, sevoflurane, methoxyflurane and the control substrate, aniline. Polyclonal antibodies to cytochrome P450 3a inhibited 90% of enflurane metabolism, but only 40% of methoxyflurane biotransformation in the microsomes from imidazole-pretreated rabbits. Thus isozyme 3a or a structurally similar cytochrome P450 seemed to catalyse almost all microsomal metabolism of enflurane. In addition, purified cytochrome P450 3a catalysed the metabolism of enflurane, sevoflurane and methoxyflurane, and the oxidation of these anaesthetics by cytochrome P450 3a was stimulated four-fold by cytochrome b5, a protein which serves as an alternate source of electrons for some cytochrome P450 reactions.

Metabolism of I-653 and isoflurane in swine

Fluoride ion concentrations were measured in plasma samples taken from chronically instrumented domestic swine before, immediately after, and 4 hours after exposure to either I-653 or isoflurane. Each anesthetic was administered at concentrations between 0.7 and 1.6 MAC and the total dose of anesthetic given was approximately 5.5 MAC hours for each agent. Plasma fluoride ion concentrations immediately after and 4 hours after exposure to isoflurane were approximately three times greater than values obtained in awake swine before anesthesia. In contrast, swine given I-653 had no detectable elevation in plasma fluoride concentration immediately after anesthesia, but a 17% (P less than 0.05) increase in plasma fluoride ion concentration 4 hours after anesthesia. These results imply that I-653 is metabolized less than is isoflurane in swine.

Characterization of halothane oxidation by hepatic microsomes and purified cytochromes P-450 using a gas chromatographic mass spectrometric assay

A sensitive assay for trifluoroacetic acid, the major product of the oxidative metabolism of halothane, has been developed to study the biotransformation of halothane. A selected ion monitoring gas chromatographic mass spectrometric assay measured trifluoroacetic acid levels as low as 1 microM in 100 microliter of reaction mixture. This assay was used to quantitate halothane metabolism in human and rabbit microsomal systems and with purified proteins. Trifluoroacetic acid production was examined as a function of the concentration of substrate present, the amount of microsomal protein used and the length of reaction time. Halothane metabolism in microsomes was linear for at least 30 min, and up to a microsomal protein concentration of 1 mg/ml. In rabbits, phenobarbital and imidazole induced the microsomal metabolism of halothane 7.36- and 18.2-fold, respectively. Imidazole was used because it is a potent inducer of cytochrome P-450 isozyme 3a which is also induced by ethanol. The cytochrome P-450 in microsomes from a single human subject metabolized halothane at a rate comparable to that found in microsomes from phenobarbital- and imidazole-pretreated rabbits. The purified phenobarbital and imidazole inducible cytochromes P-450, isozymes 2 and 3a, catalyzed the oxidation of halothane to trifluoroacetic acid. Cytochrome b5 stimulated the isozyme 3a-catalyzed oxidation of halothane by 19-fold, whereas isozyme 2 catalyzed oxidation was increased 4.3-fold. Antibodies to cytochrome P-450 3a inhibited halothane metabolism by 90% in microsomes from imidazole-pretreated rabbits, suggesting that isozyme 3a catalyzes halothane metabolism in imidazole-pretreated rabbits. In conclusion, the oxidation of halothane to trifluoroacetic acid by cytochrome P-450 isozymes 3a and 2 is enhanced markedly by cytochrome b5.

I-653 resists degradation in rats

The ability of rats pretreated with phenobarbital to metabolize a new volatile anesthetic, I-653, was compared with the metabolism of halothane, isoflurane, and methoxyflurane. Each anesthetic was administered for 2 hours at 1.6 MAC (inspired). Control rats were given phenobarbital but not exposed to an anesthetic. In rats pretreated with phenobarbital and exposed to I-653, fluoride ion concentrations in serum and excretion of fluoride ion and organic fluoride in the urine were almost indistinguishable from values measured in control rats. In contrast, rats pretreated with phenobarbital metabolized small but significant amounts of isoflurane. In rats pretreated with ethanol and exposed to I-653, the 24-hour excretion of urinary organic fluoride was nearly ten times greater than that observed in control rats. Marked increases in organic fluoride (as high as 1000 times control values) and/or fluoride ion were found in serum and/or urine after anesthesia of phenobarbital-pretreated rats with halothane or methoxyflurane. The relative stability of I-653 indicates that it may possess minimal toxic properties.

Chemical modification of cytochrome b5, cytochrome c and myoglobin with diethylpyrocarbonate

Cytochrome b5 is required for the cytochrome P-450 LM2 catalyzed oxidation of the anesthetic methoxyflurane. The ability of cytochrome b5 to support methoxyfluorane oxidation is affected by treatment with diethylpyrocarbonate, a reagent that at neutral pH is relatively specific for histidine residues. This inactivation of cytochrome b5 is reversed with hydroxylamine, which also suggests but does not prove histidine involvement. The studies reported in this paper were undertaken to determine whether histidine modification was involved in the decrease in effectiveness of cytochrome b5, or whether the inactivation could be attributed to modification of another amino acid. Our experiments demonstrate that diethylpyrocarbonate inactivates detergent-solubilized cytochrome b5 by modifying the axial histidines and displacing the heme. Because of the unexpected ease with which diethylpyrocarbonate displaced the heme from cytochrome b5, this same process was investigated in two other hemoproteins, cytochrome c and myoglobin. Diethylpyrocarbonate could not dissociate the heme from cytochrome c, whereas the heme was lost from myoglobin even more readily than from cytochrome b5.

Modification of trypsin-solubilized cytochrome b5, apocytochrome b5, and liposome-bound cytochrome b5 by diethylpyrocarbonate

The interactions of diethylpyrocarbonate (DEP) with the various forms of cytochrome b5 were studied to gain a better understanding of the factors that influence the extent of modification of the axial histidines of cytochrome b5. Very low concentrations of DEP were able to decrease the heme binding capacity of apocytochrome b5. Moreover, it was shown that two additional histidines, presumed to be the axial ligands (His 39 and 63), were modified in the apo but not the holo form of a given preparation of cytochrome b5. Trypsin-solubilized bovine cytochrome b5 was resistant to the effects of DEP. A 200-fold molar excess of DEP displaced only 15% of the heme in the trypsin-solubilized protein in contrast to an 84% displacement of the heme in the detergent-solubilized protein. However, detergent-solubilized cytochrome b5 which had been incorporated into phospholipid vesicles exhibited the same reactivity with DEP as did the trypsin-solubilized protein. This is attributed to the fact that the two resistant preparations of cytochrome b5 are monomeric in their respective environments while detergent-solubilized cytochrome b5 is known to exist as an octamer in aqueous solutions. Our studies suggest that dissociation of the octamer to the monomer results in a conformational change that decreases the reactivity of the axial ligands of the hydrophilic heme-containing domain of cytochrome b5. Examination of the cytochrome b5 molecule by computer graphics indicates that a tunnel leads from the surface of the molecule to axial histidine 63 and that axial histidine 39 is buried.

Effect of serum albumin on siderophore-mediated utilization of transferrin iron

The effect of serum and serum proteins on enterobactin- and aerobactin-mediated utilization of transferrin iron has been investigated. Serum was found to impede transfer of iron from iron transferrin to enterobactin and from [55Fe]ferric enterobactin to cells of Escherichia coli BN3040 Na 1R iuc . In contrast, serum had essentially no effect on the rate of these reactions mediated by aerobactin. Three purified serum proteins, human serum albumin, bovine serum albumin, and human immunoglobulin, were comparable to human serum in their selective ability to interfere with the transfer of 55Fe from [55Fe]ferric enterobactin to E. coli BN3040 Na 1R iuc . The inhibitory effect of human serum albumin on the enterobactin-mediated transfer of iron from [55Fe]transferrin was enhanced by preincubation of the protein with the siderophore. Pretreatment of the bacterial cells with human serum albumin did not affect the rate of utilization of siderophore iron. A linear, reciprocal relationship was found to hold for human albumin concentration vs. the first-order rate constant ( kobsd ) for the velocity of iron transfer from iron transferrin to enterobactin. Binding of serum albumin to enterobactin increased the intensity of the near-ultraviolet absorption band of the siderophore and shifted it to longer wavelengths. The stoichiometry of binding to human and bovine serum albumins was established as 1:1, and the binding constant for both enterobactin and ferric enterobactin was estimated to be in the range 1 X 10(4)-1.2 X 10(5) M-1. These results indicate that serum albumin may act synergistically with other factors in the serum, such as transferrin, to limit iron supply and in this way restrict the growth of invading microorganisms.

Aerobactin-mediated utilization of transferrin iron

Aerobactin and enterobactin, hydroxamate- and catechol-type siderophores, respectively, were found capable of removing iron (III) from transferrin in buffered solution. Although under these conditions aerobactin displaced the iron much more slowly than did enterobactin, the rate for the former could be accelerated by addition of pyrophosphate as mediator. Transfer of iron (III) from transferrin to aerobactin appeared to proceed via a ternary complex. Cells of Escherichia coli BN 3040 NalR iuc containing transport systems for both enterobactin and aerobactin, the genetic determinants for the latter specified on a ColV-type plasmid, took up iron from [55Fe]transferrin in minimal medium. In this case aerobactin was effective at a much lower concentration, although enterobactin still displayed superior ability to transfer the iron. In serum, however, the rate measured with aerobactin exceeded that found with enterobactin. The results indicate that aerobactin, in spite of its relatively unimpressive affinity for iron (III) as a siderophore, is nonetheless equipped with structural features or properties that enhance its ability to remove the metal ion from transferrin, especially when receptor-bearing cells of E. coli are present to act as a thermodynamic sink for the iron. These attributes of the aerobactin system of iron assimilation may account for its status as a virulence determinant in hospital isolates of E. coli.

Iron transfer form transferrin to ferritin mediated by polyphosphate compounds

We have studied iron transfer from transferrin to ferritin in the presence of ATP, GTP, ADP, AMP and 2,3-diphosphoglycerate. These compounds, with the exception of AMP, can release iron from transferrin at pH 7.4 and form a stable Fe(III)-phosphate complex. From these complexes, only a limited number of Fe(III) atoms can be incorporated into ferritin. Ascorbate enhances iron transfer from transferrin to ferritin at the beginning of the process but subsequently inhibits further iron deposition in ferritin.

Studies on the mechanism of pyrophosphate-mediated uptake of iron from transferrin by isolated rat-liver mitochondria

1. Respiring rat liver mitochondria accumulate iron released from transferrin by pyrophosphate. The amount of iron accumulated is 1--1.5 nmol mg protein-1 h-1, or approximately 60% of the amount of iron mobilized from transferrin. 2. The uptake declines if respiration is inhibited, substrate is deleted, or the experiments are run under anaerobic conditions. Substrate depletion and respiratory inhibitors are less inhibitory under anaerobic conditions. 3. More than 80% of the amount of iron accumulated by aerobic, actively respiring mitochondria can be chelated by bathophenanthroline sulphonate, and with deuteroporphyrin included, up to 30% of the amount of iron accumulated is recovered as deuteroheme. Iron accumulated by respiration-inhibited mitochondria under aerobic conditions is not available for heme synthesis. 4. With time the uptake of iron increases eightfold relative to the uptake of pyrophosphate. 5. The results are compatible with a model in which ferric iron is mobilized from transferrin by pyrophosphate, ferric iron pyrophosphate is bound to the mitochondria, iron is reduced, dissociates from pyrophosphate and is taken up by the mitochondria. Ferrous iron thus formed is available for heme synthesis.

Uptake of iron from transferrin by isolated rat-liver mitochondria mediated by phosphate compounds

1. Isolated rat-liver mitochondria accumulate iron from transferrin at neutral pH by a mechanism which is markedly stimulated by small-molecular-weight polyphosphate compounds. The efficiency of the phosphate compounds decreases in the order: pyrophosphate > ATP > GTP > 2,3-bis-(phospho)glycerate > phosphate. 2. The uptake has a very low energy dependence, and it does not depend on the hydrolysis of ATP or the saturation of transferrin, but it increases in parallel to the concentration of iron to reach a saturation level of 800-1200 pmol iron/mg protein. 3. Following a chase with unlabelled transferrin (125I)-labelled transferrin bound to the mitochondria remains constant, whereas the progressive uptake of 59Fe levels off. 4. During reincubation of iron-loaded mitochondria up to 30% of the iron is mobilized in the presence of ascorbate and ATP (or apotransferrin). 5. The results suggest that iron is mobilized from transferrin by the polyphosphate compounds outside the mitochondria in a subsequent reaction.