A new monoclonal antibody, KP1, raised against a lysosomal fraction of human lung macrophages, recognises a fixation-resistant epitope in a wide variety of tissue macrophages (such as Kupffer cells germinal centre, splenic, and lamina propria macrophages), and in granulocyte precursors. Its broad reactivity with cells of the mononuclear phagocytic lineage was established by testing on routinely processed samples of normal and reactive lymphoid tissues. Interdigitating reticulum cells were unstained or showed limited cytoplasmic staining while Langerhans' cells and follicular dendritic reticulum cells were unreactive. KP1 recognises a molecule of about 110 kilodaltons in macrophage-rich human tissue when tested by either immunoprecipitation or Western blotting (although the latter procedure also shows two additional components with molecular weights of 70 and 40 kilodaltons). KP1 should be of considerable value for studying disorders of the monocyte/macrophage system, including both reactive and neoplastic states (such as true histiocytic proliferations).
Carbaporphyrin ketals are porphyrinoid compounds in which a pyrrole ring of a typical porphyrin macrocycle has been replaced by a ketal-substituted indene ring. It was recently demonstrated that these compounds are effective in vitro against Leishmania tarentolae. Their in vitro effectiveness is increased when they are exposed to visible light; they act as photosensitizers capable of mediating the production of reactive oxygen species (ROS). Following on this evidence, the effectiveness and cytotoxicity of the dimethyl and diethyl carbaporphyrin ketals (CKOMe and CKOEt, respectively) were determined in vitro using pathogenic Leishmania species with and without exposure to visible light (2 and 4 h). The effectiveness against various pathogenic Leishmania species was determined to be in a micromolar range. Additionally, the effect of encapsulating the carbaporphyrin ketals in liposome formulations was tested. Liposomal delivery diminished their toxicity, while the effectiveness was enhanced upon exposure to visible light (photodynamic effect). The cytotoxicity levels for human U937 cells and hamster peritoneal macrophages were in the ranges of 0.3 to 9 M and 7 to 330 M, respectively. When tested in vivo, using a hamster (Mesocricetus auratus) model of cutaneous leishmaniasis, CKOMe was active even in the dark, suggesting that the compound, once metabolized in the animal tissue, produces an active ingredient that does not seem to be photosensitive. Reduction in lesion size, histopathologic analyses, and smears confirmed the in vivo effectiveness of the compound, since the parasitic load was diminished without noticeable toxic effects.
Coproporphyrinogen oxidase (copro'gen oxidase), which catalyses the conversion of coproporphyrinogen-III via a monovinylic intermediate to protoporphyrinogen-IX, is one of the least well
understood enzymes in the heme biosynthetic pathway. To develop a model for the substrate
recognition and binding recognition for this enzyme, a series of substrate analogues were prepared
with two alkyl substituents on positions 13 and 17 in place of the usual propionate residues.
Although the required substrate probes are porphyrinogens (hexahydroporphyrins), the corresponding porphyrin methyl esters were initialy synthesized via a,c-biladiene intermediates. These
were hydrolyzed and reduced with 3% sodium amalgam to give the unstable porphyrinogens needed
for the biochemical investigations. These modified structures were metabolized by avian preparations of copro'gen oxidase to give monovinylic products, but the second propionate residue was not
further metabolized. In three cases, the metabolites were isolated and further characterized by
proton NMR spectroscopy and mass spectrometry. When methyl or ethyl groups were placed at
the 13 and 17 positions, the resulting porphyrinogens were very good substrates (although the
ethyl version, mesoporphyrinogen-VI, gave slightly better results), but when propyl units were
introduced metabolism was significantly inhibited and the butyl-substituted structure was only
slightly transformed after long incubation periods. These results suggest the presence of an active-site lipophobic region near the catalytic site for copro'gen oxidase. The observation that the related
3-vinyl- and 3-ethylporphyrinogens with 13,17-diethyl substituents were not substrates for this
enzyme confirmed the need for a second propionate residue to hold the substrate in place at the
catalytic site.
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