Omentum facilitates liver regeneration.

Department of Medicine, Stroger Hospital of Cook County, 637 South Wood St, Durand Bldg 2nd Floor, Chicago IL 60612, United States.
World Journal of Gastroenterology (Impact Factor: 2.37). 04/2009; 15(9):1057-64.
Source: PubMed


To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats were omentectomized; in another group the omentum was left in situ and was not activated, and in the third group the omentum was activated by polydextran particles.
We pre-activated the omentum by injecting polydextran particles and then made a small wedge wound in the rat liver to allow the omentum to fuse to the wound. We monitored the regeneration of the liver by determining the ratio of liver weight/body weight, by histological evaluation (including immune staining for cytokeratin-19, an oval cell marker), and by testing for developmental gene activation using reverse transcription polymerase chain reaction (RT-PCR).
There was no liver regeneration in the omentectomized rats, nor was there significant regeneration when the omentum was not activated, even though in this instance the omentum had fused with the liver. In contrast, the liver in the rats with the activated omentum expanded to a size 50% greater than the original, and there was histologically an interlying tissue between the wounded liver and the activated omentum in which bile ducts, containing cytokeratin-19 positive oval cells, extended from the wound edge. In this interlying tissue, oval cells were abundant and appeared to proliferate to form new liver tissue. In rats pre-treated with drugs that inhibited hepatocyte growth, liver proliferation was ongoing, indicating that regeneration of the liver was the result of oval cell expansion.
Activated omentum facilitates liver regeneration following injury by a mechanism that depends largely on oval cell proliferation.

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    • "Once activated, the flimsy sheet like organ enlarges in size and mass wherein the new cells are predominantly non-fat stromal cells [23], [24]. These stromal cells are a rich source of growth factors like fibroblast growth factor (FGB) and vascular endothelial growth factor (VEGF) and express adult stem cell markers including SDF-1α, CXCR4, WT-1, as well as pluripotent embryonic stem cell markers, Nanog, Oct-4, and SSEA-1 [23], [25], [26]. Further, they were engrafted in injured tissues showing that they function as stem cells in vivo [23], [25]. "
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    ABSTRACT: The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells. Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.
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    • "Adipocytes derived from mesodermal stem cells were the first to differentiate from i.p. bone chips. This may reflect the recent observation that vascular omentum is a suitable stem cell niche8 and that the inflammatory milieu can facilitate liver regeneration.9 Adipocytes are known potent sources of nutrition and vascular endothelial growth factor and share a common progenitor with endothelial cells.10 "
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