bacteriochlorophylls and bacteriochlorin-a

Photodynamic therapy (PDT) with bacteriochlorin a(BCA) has proved to be a successful treatment for many cancers and to be cytocidal for different cell lines in culture. The present study aimed to investigate in vitro the potential of this treatment for killing lens epithelial cells (LECs) left in the human capsular bag after extracapsular cataract extraction (ECCE). Capsular bags were prepared from donor eyes using an ECCE procedure and incubated in various concentrations of bacteriochlorin a(1.6-50 microg ml(-1)) during various incubation periods (2-10 min). Subsequently, the capsules were illuminated during various exposure times (2-15 min) with a diode laser (wavelength 760 nm). After treatment, the capsular bags were cultured for 7 days in Eagle's minimal essential medium supplemented with 2% fetal calf serum. The specimens were fixed in glutaraldehyde/paraformaldehyde and examined with routine light microscopy, Hoechst staining for DNA and transmission electron microscopy. Proliferation of LECs on the posterior capsule was assessed in flat mounts. Capsular bags receiving BCA without illumination and capsular bags receiving illumination only served as controls.BCA alone or light alone have no effect on structure and proliferative activity of LECs. At a threshold protocol of incubation in BCA at 10 microg ml(-1)for 10 min and subsequent illumination for 15 min, proliferative activity of cells is largely arrested and nearly all LECs on the capsule exhibit severe signs of apoptosis. Photodynamic therapy with bacteriochlorin a induces cell death and suppression of proliferation inlens epithelial cells and could be a promising means of prevention of posterior capsule opacification.

Topics: Adult; Aged; Apoptosis; Bacteriochlorophylls; Cataract; Cataract Extraction; Cell Division; Epithelial Cells; Humans; Lens Capsule, Crystalline; Middle Aged; Photochemotherapy; Photosensitizing Agents; Porphyrins; Postoperative Complications

The B800-820, or LH3, complex is a spectroscopic variant of the B800-850 LH2 peripheral light-harvesting complex. LH3 is synthesized by some species and strains of purple bacteria when growing under what are generally classed as "stressed" conditions, such as low intensity illumination and/or low temperature (<30 degrees C). The apoproteins in these complexes modify the absorption properties of the chromophores to ensure that the photosynthetic process is highly efficient. The crystal structure of the B800-820 light-harvesting complex, an integral membrane pigment-protein complex, from the purple bacteria Rhodopseudomonas (Rps.) acidophila strain 7050 has been determined to a resolution of 3.0 A by molecular replacement. The overall structure of the LH3 complex is analogous to that of the LH2 complex from Rps. acidophila strain 10050. LH3 has a nonameric quaternary structure where two concentric cylinders of alpha-helices enclose the pigment molecules bacteriochlorophyll a and carotenoid. The observed spectroscopic differences between LH2 and LH3 can be attributed to differences in the primary structure of the apoproteins. There are changes in hydrogen bonding patterns between the coupled Bchla molecules and the protein that have an effect on the conformation of the C3-acetyl groups of the B820 molecules. The structure of LH3 shows the important role that the protein plays in modulating the characteristics of the light-harvesting system and indicates the mechanisms by which the absorption properties of the complex are altered to produce a more efficient light-harvesting component.

Topics: Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Crystallization; Crystallography, X-Ray; Hydrogen Bonding; Light-Harvesting Protein Complexes; Models, Molecular; Photosynthetic Reaction Center Complex Proteins; Porphyrins; Protein Structure, Secondary; Rhodopseudomonas