Cationic porphyrins bearing diazolium rings: synthesis and their interaction with calf thymus DNA.
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Two novel cationic porphyrins bearing five-membered rings at the meso-positions, meso-tetrakis(1,3-dimethylimidazolium-2-yl)porphyrin (H2TDMImP) and meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (H2TDMPzP), have been synthesized. These two compounds interact with calf thymus DNA (CTDNA) in different binding modes from that of mesotetrakis(N-methylpyridinium-4-yl)porphyrin (H2TMPyP). H2TDMImP outside binds to the minor groove of CTDNA while H2TDMPzP intercalates into CTDNA. These two novel cationic porphyrins strongly bind to CTDNA even at high ionic strength and the binding constant of H2TDMPzP to CTDNA is comparable to that of H2TMPyP. The binding of H2TDMImP to CTDNA is enthalpically driven. The favorable free energy changes in binding of H2TDMPzP to CTDNA come from the large negative enthalpy changes accompanied by small positive entropy changes. (+info)
Photodynamic tissue adhesion with chlorin(e6) protein conjugates.
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PURPOSE: To test the hypothesis that a photodynamic laser-activated tissue solder would perform better in sealing scleral incisions when the photosensitizer was covalently linked to the protein than when it was noncovalently mixed. METHODS: Conjugates and mixtures were prepared between the photosensitizer chlorin(e6) and various proteins (albumin, fibrinogen, and gelatin) in different ratios and used to weld penetrating scleral incisions made in human cadaveric eyes. A blue-green (488-514 nm) argon laser activated the adhesive, and the strength of the closure was measured by increasing the intraocular pressure until the wound showed leakage. RESULTS: Both covalent conjugates and noncovalent mixtures showed a light dose-dependent increase in leaking pressure. A preparation of albumin chlorin(e6) conjugate with additional albumin added (2.5 protein to chlorin(e6) molar ratio) showed significantly higher weld strength than other protein conjugates and mixtures. CONCLUSIONS: This is the first report of dye-protein conjugates as tissue solders. These conjugates may have applications in ophthalmology. (+info)
Resonance Raman effect in mu-oxo-bis[iron(III) tetraphenylporphyrin].
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Resonance Raman spectra of mu-oxo-bis[iron(III) tetraphenylporphyrin] have been observed and compared to Raman spectra of the monomers iron(III) tetraphenylporphyrin chloride and bis(piperidine)iron(II) tetraphenylporphyrin. Selection rules for the Raman effect under conditions of resonance of the incident photons with electronic states are presented for the exact symmetry group (C2) and the pseudo-symmetry group (D4d): emphasis is placed on the physical processes involved in scattering via vibronic states of the dimer. These two models are experimentally distinguishable in the behavior of the depolarization ratios of the dimer vibrational doublets. Experimental data favor the assignment of D4d as the symmetry group relevant to a description of the various states of the dimer. The usefulness of resonance Raman spectra of the mu-oco-dimer of Fe(III) tetraphenylporphyrin has been discussed with respect to several biochemical systems where there is strong evidence of two or more closely interacting chromophores. (+info)
Nuclear factor-kappaB activation by the photochemotherapeutic agent verteporfin.
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The nuclear factor-kappa B (NF-kappaB) gene transactivator serves in the formation of immune, inflammatory, and stress responses. In quiescent cells, NF-kappaB principally resides within the cytoplasm in association with inhibitory kappa (IkappaB) proteins. The status of IkappaB and NF-kappaB proteins was evaluated for promyelocytic leukemia HL-60 cells treated at different intensities of photodynamic therapy (PDT). The action of the potent photosensitizer, benzoporphyrin derivative monoacid ring A (verteporfin), and visible light irradiation were assessed. At a verteporfin concentration that produced the death of a high proportion of cells after light irradiation, evidence of caspase-3 and caspase-9 processing and of poly(ADP-ribose) polymerase cleavage was present within whole cell lysates. The general caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) effectively blocked these apoptosis-related changes. Recent studies indicate that IkappaB proteins may be caspase substrates during apoptosis. However, the level of IkappaBbeta was unchanged for HL-60 cells undergoing PDT-induced apoptosis. IkappaBalpha levels decreased during PDT-induced apoptosis, though ZVAD.fmk did not affect this change. At a less intensive level of photosensitization, cellular IkappaBalpha levels were transiently depressed after PDT. At these times, p50 and RelA NF-kappaB species were increased within nuclear extracts, as revealed by electrophoretic mobility supershift assays. HL-60 cells transiently transfected with a kappaB-luciferase reporter construct exhibited elevated luciferase activity after PDT or treatment with tumor necrosis factor-alpha, a well-characterized NF-kappaB activator. Productive NF-kappaB activation and associated gene transcription may influence the phenotype and behavior of cells exposed to less intensive PDT regimens. However, IkappaBalpha is not subject to caspase-mediated degradation as a component of PDT-induced apoptosis. (Blood. 2000;95:256-262) (+info)
Harmonic and anharmonic dynamics of Fe-CO and Fe-O(2) in heme models.
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We present density-functional molecular dynamics simulations of FeP(Im)(AB) heme models (AB = CO, O(2), Im = imidazole) as a way of sketching the dynamic motion of the axial ligands at room temperature. The FeP(Im)(CO) model is characterized by an essentially upright FeCO unit, undergoing small deviations with respect to its linear equilibrium structure (bending and tilting up to 10 degrees and 7 degrees, often occur). The motion of the carbon monoxide ligand is found to be quite complex and fast, its projection on the porphyrin plane sampling all the porphyrin quadrants in a short time ( approximately 0.5 ps). Simultaneously, the imidazole ligand rotates slowly around the Fe-N(epsilon) bond. In contrast to carbon monoxide, the oxygen ligand in FeP(Im)(O(2)) prefers a conformation where the projection of the O-O axis on the porphyrin plane bisects one of the porphyrin quadrants. A transition to other quadrants takes place through an O-O/Fe-N(p) overlapping conformation, within 4-6 ps. Further details of these mechanisms and their implications are discussed. (+info)
Targeting of HIV gp120 by oligonucleotide-photosensitizer conjugates. Light-induced damages.
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Some guanine-rich oligonucleotides inhibit HIV infectivity through interaction with the gp120 glycoprotein. Besides, photoinactivation of viruses attracts attention for blood decontamination. The feasibility of targeting a red light-absorbing chlorin-type photosensitizer to gp120 through covalent coupling with 8-mer phosphodiester oligodeoxynucleotides is investigated. Some conjugates inhibit binding of antibodies directed to gp120. Inhibition is significantly increased upon red light activation. The activity of the conjugates correlates with their ability to self-associate, a process strongly favored by the propensity of the hydrophobic chlorin moiety to dimerize. Thus, the photosensitizer moiety both promotes structures with a higher affinity for gp120 and, upon light activation, can induce site-directed damages to the protein. (+info)
In vivo fluence rate and fractionation effects on tumor response and photobleaching: photodynamic therapy with two photosensitizers in an orthotopic rat tumor model.
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The effect of fluence rate and light fractionation on phototoxicity was investigated in vivo in an orthotopic rat bladder tumor model. Two photosensitizers, benzoporphyrin derivative monoacid ring A and 5-aminolevulinic acid-induced protoporphyrin IX, were studied. For a given cumulative light dose of 30 J/cm2, enhanced tumor destruction was observed from both photosensitizers when using either lower fluence rates or fractionated light delivery. Photobleaching experiments in vivo demonstrated that the photobleaching rate, however, was not fluence rate dependent. The fluence rate and light fractionation effects on tumor phototoxicity lead to rapid local depletion in oxygen concentration that inhibited subsequent photochemical reactions necessary for efficient photodestruction of tumor cells. Nicotinamide did not enhance photodynamic therapy efficacy, suggesting that the added increase of oxygen within the tumor was not sufficient to enhance photodestruction of hypoxic cell fractions. The independence of the photobleaching rate with fluence rate suggests distinct mechanisms, at least in part, of photodestruction of the tumor and the photosensitizer and that the rate of photosensitizer photo-bleaching may not always be an appropriate monitor for singlet oxygen availability and photodynamic therapy dosimetry. (+info)
Use of heme compounds as iron sources by pathogenic neisseriae requires the product of the hemO gene.
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Heme compounds are an important source of iron for neisseriae. We have identified a neisserial gene, hemO, that is essential for heme, hemoglobin (Hb), and haptoglobin-Hb utilization. The hemO gene is located 178 bp upstream of the hmbR Hb receptor gene in Neisseria meningitidis isolates. The product of the hemO gene is homologous to enzymes that degrade heme; 21% of its amino acid residues are identical, and 44% are similar, to those of the human heme oxygenase-1. DNA sequences homologous to hemO were ubiquitous in commensal and pathogenic neisseriae. HemO genetic knockout strains of Neisseria gonorrhoeae and N. meningitidis were unable to use any heme source, while the assimilation of transferrin-iron and iron-citrate complexes was unaffected. A phenotypic characterization of a conditional hemO mutant, constructed by inserting an isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated promoter upstream of the ribosomal binding site of hemO, confirmed the indispensability of the HemO protein in heme utilization. The expression of HemO also protected N. meningitidis cells against heme toxicity. hemO mutants were still able to transport heme into the cell, since both heme and Hb could complement an N. meningitidis hemA hemO double mutant for growth. The expression of the HmbR receptor was reduced significantly by the inactivation of the hemO gene, suggesting that hemO and hmbR are transcriptionally linked. The expression of the unlinked Hb receptor, HpuAB, was not altered. Comparison of the polypeptide patterns of the wild type and the hemO mutant led to detection of six protein spots with an altered expression pattern, suggesting a more general role of HemO in the regulation of gene expression in Neisseriae. (+info)