Stem Cell Therapy and Hydrogen Sulfide: Conventional or Nonconventional Mechanisms of Action?

Hydrogen sulfide (H2S) has many beneficial biological properties, including the ability to promote vasodilation. It has been shown to be released from stem cells and increased by hypoxia. Therefore, H2S may be an important paracrine factor in stem cell-mediated intestinal protection. We hypothesized that H2S created through conventional pathways would be a critical component of stem cell-mediated intestinal protection after ischemic injury. Human bone marrow-derived mesenchymal stem cells (BMSCs) were transfected with negative control siRNA (Scramble), or with siRNA to CBS, MPST, or CTH. Knockdown was confirmed with PCR and H2S gas assessed with AzMC fluorophore. Eight-week-old male mice then underwent intestinal ischemia for 60 min, after which time, perfusion was restored. BMSCs from each of the above groups were then placed into the mouse abdominal cavity before final closure. After 24 h, mice were reanesthetized and mesenteric perfusion was assessed by Laser Doppler Imaging (LDI). Animals were then sacrificed and intestines excised, placed in formalin, paraffin embedded, and stained with H & E. Intestines were then scored with a common mucosal injury grading scale. PCR confirmed knockdown of conventional H2S-producing enzymes (CBS, MPST, CTH). H2S gas was decreased in MPST and CTH-transfected cells in normoxic conditions, but was not decreased compared with Scramble in any of the transfected groups in hypoxic conditions. BMSCs promoted increased mesenteric perfusion at 24 h postischemia compared with vehicle. Transfected stem cells provided equivalent protection. Histologic injury was improved with BMSCs compared with vehicle. CBS, MPST, and CTH knockdown cell lines did not have any worse histological injury compared with Scramble. Knocking down conventional H2S-producing enzymes only impacted gas production in normoxic conditions. When cells were transfected in hypoxic conditions, as would be expected in the ischemic intestines, H2S gas was not depressed. These data, along with unchanged perfusion and histological injury parameters with conventional enzyme knockdown, would indicate that alternative H2S production pathways may be initiated during hypoxic and/or ischemic events.