Background: There is an increasing local application of methylene blue (MB) in the treatment
of discogenic low back pain (LBP) and percutaneous transforaminal endoscopic discectomy
(PTED) procedures. MB could generate DNA damage and induce apoptosis in different cell types;
however, the effects of MB on intervertebral disc (IVD) annulus fibrosus (AF) cells are not clearly
understood.
Objective: The objective of this study was to investigate the effects of different concentrations
of MB on rat AF cells in vitro.
Study Design: This study used an experimental design.
Setting: This research was conducted at the Orthopaedic Institute of the Clinical Medical College
of Yangzhou University.
Methods: AF cells were isolated and cultured with different concentrations of MB (0, 2, 20, and
200 μg/mL) and assessed to determine the possible cytotoxic effects of MB. The cell proliferation
was detected by Cell Counting Kit-8 (CCK-8) assay. The inverted phase-contrast microscopy
was used to perform morphological observation of apoptotic cells, and flow cytometry was
used to measure the incidence of cell apoptosis. The mRNA and protein expression levels of
apoptosis-associated genes (caspase-3, Bcl-2, and Bax) and other related genes (collagen type
I, transforming growth factor β1 [TGF-β1], fibroblast growth factor [bFGF], and tissue inhibitor
of metalloproteinase-1 [TIMP-1]) were analyzed by quantitative real-time PCR (RT-PCR) and
Western blotting.
Results: Our results indicated that MB reduced cell viability in a concentration- and timedependent manner. MB also induced marked AF cell apoptosis in a concentration-dependent
manner observed by inverted phase-contrast microscopy, flow cytometry, and indicated by the
increased expression of caspase-3. Both RT-PCR and Western blotting revealed significant upregulation of Bax and caspase-3 expression levels accompanied by decreased expression of Bcl2 in a concentration-dependent manner. Moreover, collagen type I, TGF-β1, bFGF, and TIMP-1
mRNA and protein levels were also found to be decreased by MB in a concentration-dependent
manner.
Limitations: Limitations of this study were the in vitro study design and lack of in vivo validation
of the observed effects of MB on human IVD cells.
Conclusions: Our results indicate that a high concentration of MB can not only inhibit proliferation
and paracrine function of AF cells, but can also induce cell apoptosis in a concentration-dependent
manner, suggesting that it is necessary to choose low concentrations of MB in practical application
and limit the use of MB in the treatment of discogenic LBP to research protocols.
Key words: Methylene blue, annulus fibrosus cell, proliferation, apoptosis, paracrine
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