ANALYSIS OF THE MECHANISM OF PHOTODYNAMIC INDUCTION OF SYNTHESIS OF A POLYPEPTIDE IN ARTHROBACTER SP.

Synthesis of a 21000-dalton polypeptide is greatly stimulated in a species of Arthrobacter by the combined influence of light, oxygen and a sensitizing dye. The dye must enter the cells for the effect to occur. The extent of photoinduction was not enhanced in the presence of D₂O nor was it significantly inhibited by 10–20 mM azide or 1,4-diazabicyclo [2.2.2]octane. The phenazine dye neutral red was nearly as effective as methylene blue and rose bengal in sensitizing photoinduction, although neutral red was inactive as a sensitizer of the photooxidation of histidine or methionine, singlet oxygen-mediated reactions. Thus, generation of singlet oxygen does not seem to be a necessary step in the mechanism of induction. Neutral red had low activity as a sensitizer of the oxidation of sulfite, which proceeds by a radical mechanism. Considering also the known properties of phenazine compounds, the evidence supports the involvement of radical intermediates in the mechanism of photoinduction. Furthermore, the results suggest that the dyes must interact directly with an intracellular component, possibly DNA, for induction to occur.     

Influence of structure on binding of chlorophylls to peptide ligands

Four classes of chlorophyll (Chl), a, b, c, and d, are involved in photosynthesis within cyanobacteria, algae, and plants. These classes have different evolutionary origins, chemical properties, and biological functions. Our results demonstrate that peptide-bound ligands provided by the imidazole group of histidine and the charge-compensated glutamate-arginine ion pair readily form coordination bonds with Chls a and d but do not interact significantly with Chls b and c. These ligands are apparently not sufficiently strong Lewis bases to displace strongly coordinated water from Chls b and c. These differences determine specificity of binding of Chls in light-harvesting complexes and play an important role in assembly of stable Chl-protein complexes, which has had a profound impact on the evolution of photosynthetic organisms.     

PHOTODYNAMIC SENSITIZERS FROM CHLOROPHYLL:PURPURIN–18 AND CHLORINp6

Abstract— Two easily prepared derivatives of chlorophyll,purpurin–18 and chlorin p ₆, are potent sensitizers of cell killing by low-intensity red light. The internal anhydride group inpurpurin–18 provides the potential of covalently linking in one step the chlorin to cell targeting agents such as antibodies.     

SIMILARITIES IN THE INDUCTION OF SYNTHESIS OF A CELL-SURFACE POLYPEPTIDE IN Arthrobacter sp. BY NEAR-UV IRRADIATION and PHOTODYNAMIC CONDITIONS

Irradiation of aerobic suspensions of Arthrobacter sp. with near-UV light (310-400 nm) induced synthesis of a 21 000 dalton, cell-surface polypeptide. Synthesis of this polypeptide also was induced by visible light in the presence of photodynamic dyes, as shown previously (Hoober, 1978). Induction of the polypeptide in near-UV light and with visible light plus dyes was inhibited by histidine. Hemin inhibited induction in near-UV light and in visible light with methylene blue, neutral red and acrifiavin, which are cationic dyes, but failed to inhibit induction in visible light with rose bengal, an anionic dye. These results suggested that inhibition by hemin required electrostatically favored interaction between the anionic porphyrin and the sensitizer, and that the near-UV light effect was mediated by a cationic or neutral endogenous sensitizer. The similarities in the responses of the cells to near-UV irradiation and visible light plus dyes suggested that the mechanism of induction under the two conditions was the same.     

EFFECTIVENESS OF PHOTOFRIN II IN ACIWATION OF MACROPHAGES AND in vitro KILLING OF RETINOBLASTOMA CELLS

Abstract Administration of a small dose (300 ng/mouse) of photofrin II (PII) to mice, followed by 4 days of exposure to only ambient fluorescent light in animal quarters, induced Fc-receptor-mediated phagocytic and superoxide-generating capacities of peritoneal macrophages by five- and seven-fold, respectively. When these mice were kept in the dark for 4 days, no activation of macrophages was observed. These results suggest that macrophage activation is a consequence of photodynamic activation. Much higher doses (> 3000 ng/mouse) suppressed macrophage activity. However, 2 months after administration of 3000 ng PII/mouse, greatly enhanced phagocytic and superoxide-generating capacities of peritoneal macrophages were observed.
In vitro photodynamic activation of macrophages was analyzed after white or red fluorescent light exposure of mouse peritoneal cells (mixture of macrophages and B and T lymphocytes) in media containing PII. A short (10 s) white fluorescent light treatment of peritoneal cells in a medium containing 0.03 ng PII/mL produced the maximal level of phagocytic activity of macrophages. Illumination with the same total fluence of red fluorescent light requires a threefold higher concentration of PII to achieve the same extent of enhanced phagocytic activity of macrophages. Thus, photodynamic activation of macrophages with PII by white fluorescent light was more efficient than by red fluorescent light. Similarly, photodynamic killing of retinoblastoma cells was more efficient with white than red fluorescent light. The concentration of hematoporphyrin (HP) or PII required for direct photodynamic killing of retinoblastoma cells was roughly four orders of magnitude greater than that required for activation of macrophages. These results suggest that effective photodynamic therapy may be achieved with milder treatments that stimulate macrophage activity, an important component of immunopotentiation.     

TUMORICIDAL CAPACITIES OF MACROPHAGES PHOTODYNAMICALLY ACTIVATED WITH HEMATOPORPHYRIN DERIVATIVE

Four days after administration to mice of small amounts (30-600 ng/mouse) of hematoporphyrin derivative (HPD), peritoneal macrophages exhibited a greatly enhanced Fc-receptor mediated phagocytic capacity as assayed by ingestion activity of IgG-coated sheep erythrocytes. Much higher doses (greater than 3000 ng/mouse) did not have this effect. The peritoneal macrophages activated by administration of HPD have tumoricidal capacity for IgG-coated retinoblastoma cells. We then studied in vitro photodynamic activation of macrophages by white and red fluorescent light irradiation of mouse peritoneal cells (mixture of macrophages and B and T lymphocytes) in media containing very low concentrations of HPD. A short (5 s) white fluorescent light exposure (1Wm-2) of peritoneal cells in a medium containing 0.03 ng HPD/mL produced the maximal level of ingestion activity of macrophages. A 15 s red fluorescent light exposure (1Wm-2) of peritoneal cells in a medium containing 0.1 ng HPD/mL produced the maximal level of ingestion activity of macrophages. Thus, photodynamic activation of macrophages with white fluorescent light is more efficient than that with red fluorescent light. This can be explained by the fact that HPD has a large absorption peak at about 364 nm which extends into the visible range, and decreasingly smaller absorption bands at 500, 535, 570 and 630 nm. In vitro photodynamically activated macrophages showed efficient tumoricidal activity regardless of the type (white or red) of light used. These results suggest that a low level of HPD promotes therapeutic immunopotentiation.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Beta-delayed proton emitter kr

The nucleide ⁷³Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10⁻³ proton/decay. The protons populate the ground state and also the first excited 2⁺ state at 866 keV in ⁷²Se with a relative intensity of (35±9) %. The value of Q_EC−B_p, where B_p is the proton separation energy for the nucleus ⁷³Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay.