Knockdown of Osteopontin Reduces the Inflammatory Response and Subsequent Size of Postsurgical Adhesions in a Murine Model

Adhesions between organs after abdominal surgery remain a significant unresolved clinical problem, causing considerable postoperative morbidity. Osteopontin (OPN) is a cytokine up-regulated after cell injury and tissue repair. Our previous studies have shown that blocking OPN expression at sites of cutaneous wounding resulted in reduced granulation tissue and scarring. We hypothesize that it may be possible to similarly reduce inflammation-associated fibrosis that causes small-bowel adhesions after abdominal surgery. By using a mouse model, we deliver OPN antisense oligodeoxynucleotides via Pluronic gel to the surface of injured, juxtaposed small bowel and show a significant reduction of inflammatory cell influx to the developing adhesion and a dramatic reduction in the resulting adhesion size. A significant reduction in α-smooth muscle actin expression and collagen deposition within the mature adhesion is also demonstrated. We see no impact on mortality, and the healing of serosal injury to intact bowel appeared normal given the reduced inflammatory response. Our studies suggest that dampening OPN levels might be a potentially important target for anti-adhesion therapeutics.The peritoneum is an extensive and complex organ consisting of a layer of mesothelial cells lining the peritoneal cavity and all organs within it.¹ One of the main functions of the peritoneum is to allow friction-free movement between abdominal viscera and the peritoneal wall.² Any surgery that breaches the peritoneal lining causes injury to the peritoneum, which responds by raising inflammatory signals that attract innate immune cells in parallel with a wound repair response and subsequent fibrosis.^3–5 This almost invariably results in permanent peritoneal adhesion formation.⁶ The result can be tethering of adjacent small-bowel loops that may lead to abdominal pain⁷ and/or bowel obstruction,⁸ which is a significant cause of postoperative morbidity in clinical practice. Readmission rates secondary to adhesional complications are as high as 5% to 10% after abdominal surgery.^9,10 Adhesion prevention options in clinical practice are limited to either barrier methods¹¹ or flotation fluids,¹² which use the concept of keeping damaged peritoneal surfaces separated during their healing process; however, these options are of limited effectiveness.^13,14 Pathophysiological manipulation of the cascade events leading to fibrosis has been investigated,^15–18 but none has led to a clinically usable product. Herein, we investigate whether therapeutic strategies used to block scar formation after skin healing might also be effective during peritoneal repair. Microarray studies of wound tissues from wild-type mice versus PU.1 mice (lacking neutrophils, macrophages, and mast cells) reveal an inflammation-dependent gene, osteopontin (OPN), that is expressed by wound granulation tissue fibroblasts, coincident with a skin wound inflammatory response.^19,20 PU.1 mice heal skin wounds without the standard inflammatory cascade, which results in less fibrosis and scarring at the healed wound site.¹⁹ OPN acts both as a secreted chemokine-like protein and as part of an intracellular signaling complex.²¹ It plays key roles in several processes associated with tissue repair, including cell adhesion, migration, and survival.^21,22 Short-term local knockdown of OPN in cutaneous wounds leads to decreased granulation tissue and reduced scar formation.²³ In this study, we investigate whether these effects are transferable to peritoneal repair and also might block i.p. fibrosis.