Regenerating the Anal Sphincter: Cytokines, Stem Cells, or Both?

BACKGROUND: Healing of an anal sphincter defect at a time distant from injury is a challenge.

OBJECTIVE: We aimed to investigate whether re-establishing stem cell homing at the site of an anal sphincter defect when cytokine expression has declined using a plasmid engineered to express stromal derived factor 1 with or without mesenchymal stem cells can improve anatomic and functional outcome.

DESIGN: This was a randomized animal study.

SETTINGS: Thirty-two female age- and weight-matched Sprague Dawley rats underwent 50% excision of the anal sphincter complex. Three weeks after injury, 4 interventions were randomly allocated (n = 8), including no intervention, 100-μg plasmid, plasmid and 800,000 cells, and plasmid with a gelatin scaffold mixed with cells.

MAIN OUTCOME MEASURES: The differences in anal sphincter resting pressures just before and 4 weeks after intervention were used for functional analysis. Histology was analyzed using Masson staining. One-way ANOVA followed by the Tukey post hoc test was used for pressure and histological analysis.

RESULTS: All 3 of the intervention groups had a significantly greater change in resting pressure (plasmid p = 0.009; plasmid + cells p = 0.047; plasmid + cells in scaffold p = 0.009) compared with the control group. The plasmid-with-cells group showed increased organization of muscle architecture and increased muscle percentage, whereas the control group showed disorganized architecture at the site of the defect. Histological quantification revealed significantly more muscle at the site of defect in the plasmid-plus-cells group compared with the control group, which had the least muscle. Quantification of connective tissue revealed significantly less fibrosis at the site of defect in the plasmid and plasmid-plus-cells groups compared with the control group.

LIMITATIONS: Midterm evaluation and muscle morphology were not defined.

CONCLUSIONS: At this midterm follow-up, local delivery of a stromal derived factor 1 plasmid with or without local mesenchymal stem cells enhanced anal sphincter muscle regeneration long after an anal sphincter injury, thereby improving functional outcome. See Video Abstract at https://links.lww.com/DCR/A324.