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Chlamydia pneumoniae growth inhibition in human monocytic THP-1 cells and human epithelial HEp-2 cells by a novel phenoxazine derivative

^1,2,4,5Department of Infectious Disease, Division of Microbiology¹, First Department of Internal Medicine², Laboratory of Electron Microscopy⁴ and Department of Anatomy⁵, Kyorin University School of Medicine,Tokyo 181-8611, Japan ³Division of Molecular Microbiology, Department of Basic Laboratory Sciences, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan ⁶Department of Virology I, National Institute of Infectious Diseases, Tokyo 162-8642, Japan ⁷Department of Biochemistry, Tokyo Medical University, Tokyo 160-0022, Japan

Correspondence Shigeru Kamiya skamiya{at}kyorin-u.ac.jp

Received 15 March 2005
Accepted 18 July 2005

In this study the effects of 2-amino-phenoxazine-3-one (phenoxazine derivate, Phx-3) on Chlamydia (Chlamydophila) pneumoniae growth in human monocytic THP-1 cells as well as human epithelial HEp-2 cells were examined. Cells were infected with bacteria at an m.o.i. of 10 by centrifugation. After washing to remove any remaining bacteria, the cells were incubated with or without Phx-3 in the presence or absence of tryptophan for 72 h. The bacteria in cells were assessed by staining of chlamydial inclusions with FITC-labelled anti-chlamydial antibody, electron microscopic analysis, real-time RT-PCR specific for C. pneumoniae 16S rRNA and propagation on HEp-2 cells. Treatment with Phx-3 significantly inhibited growth of C. pneumoniae in THP-1 and HEp-2 cells. A decrease in the number of bacterial 16S rRNA transcripts was also confirmed in both cell lines by real-time RT-PCR. Electron microscopic studies revealed that treatment with Phx-3 induces bacterial destruction in most of the inclusion bodies in these cells. Addition of tryptophan to the culture slightly blocked the growth inhibition of C. pneumoniae by Phx-3. The reagents did not show any cytotoxicity to the cells at the concentrations used. The results suggest that Phx-3 inhibits C. pneumoniae replication in human monocytic cells as well as epithelial cells, partially depending on the tryptophan-metabolic pathway of host cells. Thus, Phx-3 might be a useful compound for controlling C. pneumoniae growth in cells and may be an alternative conventional therapy.

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