Allicin Inhibits Proliferation and Promotes Apoptosis of Human Epidural Scar Fibroblasts

Background

Allicin can suppress liver and cardiac fibrosis; thus, we hypothesized that it might prevent scar tissue from extensive epidural fibrosis after laminectomy.

Methods

Human epidural scar fibroblasts were isolated from surgical specimens and treated with allicin at a gradient of concentrations. Morphology, viability, migration rate, cell cycle, and apoptosis rate were measured by fluorescence microscope, Cell Counting Kit-8 assay, scratch assay, and flow cytometry. Western blot was used to measure the expression level of proliferation-related proteins.

Results

After treatment by allicin, cell viability (P = 0.042) and migration rate (P = 0.010 in scratch assay and P = 0.025 in transwell assay) decreased significantly in a dose-dependent manner. The percentage of G₁ phase cells significantly decreased (P = 0.017), whereas the percentage of S phase cells (P = 0.096) and G₂ phase cells (P = 0.038) significantly increased in a dose-dependent manner. Similarly, the percentage of apoptotic cells increased significantly in a dose-dependent manner (P = 0.036). Compared with the control group, the expression level of proliferating cell nuclear antigen protein (P = 0.081) and Bcl-2 protein (P = 0.029) significantly decreased, whereas the BAX protein level significantly increased (P = 0.017).

Conclusions

Allicin can suppress human epidural scar fibroblast migration, induce cell apoptosis, and block cell proliferation at S phase and G₂ phase.

Introduction

Lumbar epidural fibrosis represents a consequence of the histopathologic wound healing process after laminectomy and discectomy. Normal epidural fibrosis helps to repair the surgical incision, whereas extensive fibrosis may compress and irritate the nerve roots, thereby inducing recurrent radicular pain.¹ Up to 95.6% of patients had extensive epidural fibrosis under epiduroscopy, and concordant pain was present in 84.3% of these patients and depended on the severity of fibrosis.² As the outcome of current treatment options, including conservative treatment and scar excision, for such patients remains poor, biological therapies are increasingly being investigated.³

Fibroblasts are the main cells affecting the process of epidural fibrosis, and their proliferation is regulated by growth factors. The extensive epidural fibrosis is primarily produced by excessive fibroblast proliferation, which extends into the neural canal and causes pressure and stimulation to spinal marrow and nerve roots.⁴ Allicin (diallyl thiosulfinate) is a biomolecule produced during mashing of garlic. It has a variety of active biological functions for microbial, plant, and mammalian cells. In mammalian cell lines, allicin can induce apoptosis and inhibits cell proliferation.⁵ Intriguingly, allicin can suppress liver fibrosis via inhibition of transforming growth factor-β1⁶ and suppress cardiac fibrosis by blocking nuclear factor-κB and Smad 2/3 signaling pathway.⁷ Notably, allicin is the main ingredient of garlic extract, the phytochemicals of which have never been associated with negative side effects.⁶ Thus, we hypothesized that allicin can inhibit proliferation and promote apoptosis of human epidural scar fibroblasts, thereby attenuating the epidural fibrosis and partly avoiding failed back surgery syndrome.