Hydrogen sulfide causes apoptosis in human pulp stem cells

Introduction

Untreated dental caries will eventually lead to pulpal inflammation. Although much is known regarding the interaction of microbial antigens and the immunologic defense systems of pulp, many aspects of the pathogenesis of pulpitis are not fully understood. The relationship between human pulp stem cells (HPSCs) and the pathogenesis of pulpitis remains among the poorly understood areas. Many of the invading bacteria are known to produce considerable amounts of hydrogen sulfide (H₂S), which causes apoptosis in some tissues. The aims of this study were to determine whether H₂S causes apoptosis in HPSCs and to examine its signaling pathway.

Methods

Stem cells were isolated from human dental pulp and incubated with 50 ng/mL H₂S for 48 hours. To detect apoptosis, the cells were analyzed by using flow cytometry. The mitochondrial signaling pathway was examined by determining mitochondrial membrane depolarization. Activation of the key apoptotic enzymes caspase-9, caspase-8, and caspase-3 was assessed by using enzyme-linked immunosorbent assay. Release of cytochrome C from mitochondria was also determined.

Results

The number of apoptotic cells increased significantly with H₂S treatment from 1.6% to 16.3% (P < .01). Significant increases were also measured in the amounts of caspase-9 and caspase-3 and in cytochrome C release (all P < .01) and in mitochondrial membrane depolarization (P < .05), whereas caspase-8 activity was not found.

Conclusions

H₂S causes apoptosis in HPSCs by activating the mitochondrial pathway. It is suggested that H₂S might be one of the factors modifying the pathogenesis of pulpitis by causing loss of viability of HPSCs through apoptosis.