The objective of this study was to evaluate physical, mechanical, and biological properties of the polydioxanone (PDO) monofilament meshes and polyglycolide (PGA) polyfilament meshes in comparison with Permacol®implants. In rat experimental model, a 1.5 × 2.0 cm defect in abdominal wall was reconstructed by using the Permacol surgical implant or knitted meshes produced from either PDO monofilament, or PGA multifilament. The implant sites were assessed for the tensile strength and the extents of material resorption, host inflammatory response and host tissue replacement on days 3, 10, 30, or 60 after the surgery. The PDO and PGA meshes were rapidly pervaded by the host connective tissue with elements of skeletal muscle histogenesis. The degree of adhesions was significantly higher in the Permacol group. All of the prostheses underwent resorption, which correlated with gradual decreases in the overall tensile strength of the site and the Col1a1 gene expression level. Elevated expression of Fgf2 gene maintained longer in the PDO group, and the Mmp9 gene expression level in this group was higher than in the other groups. Gene expression levels of inflammatory cytokines were higher in the Permacol group. The foreign body giant cell numbers were lower in the PDO and Permacol groups than in the PGA group. Minimal macrophage infiltration with predominance of M2 cells was observed in the PDO group. Overall, the PDO prosthesis turned out to be significantly better than the PGA or Permacol prostheses by a number of indicators of biocompatibility and efficacy.

In many clinical cases of extensive liver resection (e.g. due to malignancy), the residual portion is too small to maintain the body homeostasis. The resulting acute liver failure is associated with the compensatory growth inhibition, which is a typical manifestation of the 'small for size' liver syndrome. The study investigates possible causes of the delayed onset of hepatocyte proliferation after subtotal hepatectomy (80% liver resection) in rats. The data indicate that the growth inhibition correlates with delayed upregulation of the Tnf gene expression and low content of the corresponding Tnfα protein within the residual hepatic tissue. Considering the involvement of Tnf/Tnfα, the observed growth inhibition may be related to particular properties of liver macrophages - the resident Kupffer cells with CD68+CX1CR3-CD11b-phenotype.The delayed onset of hepatocyte proliferation correlates with low levels of Tnfα in the residual hepatic tissue. The observed growth inhibition possibly reflects specific composition of macrophage population of the liver. It is entirely composed of embryonically-derived Kupffer cells, which express the 'proregeneratory' M2 macrophage-specific marker CD206 in the course of regeneration.

The role of the lungs and kidneys in liver regeneration after subtotal hepatectomy was studied on a rat model. It was found that production of hepatocyte growth factor (HGF) in the lungs and kidneys and expression of cytokine genes Il1b, Il6, Il10, and tnfa significantly increased. Analysis of the dynamics of lung macrophage population showed that accumulation of HGF and the increase in the expression of cytokine genes in the lungs were accompanied by simultaneous increase in the number of CD68+ cells, which attested to the leading role of macrophages in activation of HGF synthesis in the lungs. Macrophage content in the kidneys after subtotal hepatectomy did not increase.

To investigate the influence of the umbilical cord-derived multipotent stromal cells (MSCs) on recovery of the liver after the subtotal resection, that is, removal of 80% of the organ mass, a renowned model of the small-for-size liver remnant syndrome. The MSCs were obtained from the intervascular tissue of umbilical cords, dissected from rat fetuses, by the explant culture technique. The vital labeling of MSCs with РКН26 was carried out on the 3rd passage. The subtotal resection was performed on male Sprague-Dawley rats. The experimental group animals received a transplant 106 MSCs infused into the spleen. Hepatocyte proliferation was assessed by counting of either mitotic figures or Ki67-positive cells in microscopic images. MSC differentiation was assessed with antibodies to hepatocyte-specific marker cytokeratin 18 (CK18), cholangiocyte-specific protein CK19, smooth muscle cell-specific protein α-SMA, the endothelial cell marker CD31, or the active fibroblast marker FAPα. Total macrophages of the liver were selectively stained in cryosections incubated with anti-CD68 antibodies (1:100, Abcam), while the M2a and M2c macrophage populations were selectively stained with anti-CD206 antibodies. Expression of interleukin and growth factor genes was evaluated with PCR-RT. Intrasplenic allogeneic transplantation of the umbilical cord-derived multipotent stromal cells stimulates reparative processes within the residual liver tissue after subtotal resection (removal of 80% of the organ mass), as indicated by increased rates of hepatocyte proliferation and accelerated organ mass recovery. These effects may result from paracrine influence of the transplanted cells on the resident macrophage population of the liver. The transplantation favors polarization of macrophages to M2 phenotype (the M2-polarized macrophages specifically express CD206; they are known to suppress inflammation and support tissue repair). No differentiation of the transplanted cells into any of the liver cell types have been observed in the study. We found no direct evidence for the paracrine effect of MSCs on liver regeneration after the subtotal liver resection in rats. However, the paracrine mechanism of the therapeutic activity of transplanted MSC is indirectly indicated by a decrease in the total number of CD68 + macrophages and an increase in the proportion of M2 pro-repair macrophages in the regenerating liver as compared to animals in which the transplantation was only mimicked.

The paper presents current evidence on the properties of human umbilical cord-derived mesenchymal stem cells, including origin, proliferative potential, plasticity, stability of karyotype and phenotype, transcriptome, secretome, and immunomodulatory activity. A review of preclinical studies and clinical trials using this cell type is performed. Prospects for the use of mesenchymal stem cells, derived from the umbilical cord, in cell transplantation are associated with the need for specialized biobanking and transplant standardization criteria.

Proliferation of hepatocytes is known to be the main process in the hepatectomy-induced liver regrowth; however, in cases of extensive loss it may be insufficient for complete recovery unless supported by some additional sources e.g. mobilization of undifferentiated progenitors. The study was conducted on rat model of 80% subtotal hepatectomy; the objective was to evaluate contributions of hepatocytes and resident progenitor cells to the hepatic tissue recovery via monitoring specific mRNA and/or protein expression levels for a panel of genes implicated in growth, cell differentiation, angiogenesis, and inflammation. Some of the genes showed distinctive temporal expression patterns, which were loosely associated with two waves of hepatocyte proliferation observed at 2 and 7 days after the surgery. Focusing on genes implicated in regulation of the progenitor cell activity, we came across slight increases in expression levels for Sox9 and two genes encoding tumor necrosis factor-like cytokine TWEAK (Tnfsf12) and its receptor Fn14 (Tnfrsf12a). At the same time, no increase in numbers of cytokeratin 19-positive (CK19+) cells was observed in periportal areas, and no CK19+ cells were found in hepatic plates. Since CK19 is thought to be a specific marker of both cholangiocytes and the hepatic progenitor cells, the data indicate a lack of activation of the resident progenitor cells during recovery of hepatic tissue after 80% subtotal hepatectomy. Thus, proliferation of hepatocytes invariably makes the major contribution to the hepatic tissue recovery, although in the cases of subtotal loss this contribution is distinctively modulated. In particular, induction of Sox9 and TWEAK/Fn14 regulatory pathways, conventionally attributed to progenitor cell activation, may incidentally stimulate mitotic activity of hepatocytes.

Expression of il1b, il6, il10, tnfa, hgf, tgfb, vegf, and fgf2 genes in the lungs and kidneys was examined on rat model of liver regeneration after subtotal hepatectomy. Enhanced expression of il6, il10, tnfa, hgf, and fgf2 genes was detected at the early terms after 80% liver resection.

In the liver of rats subjected to subtotal liver resection (80% organ weight), the expression of sox9 gene and SOX9 protein content increased and cells with hepatocyte morphology expressing SOX9 appeared; the proportion of cells expressing cytokeratin-19 also increased. Based on these data, we cannot completely exclude the involvement of resident progenitor cells and hepatocyte reprogramming in liver regeneration after subtotal resection, however, the contribution of these processes seems to be insignificant. The leading mechanism of liver mass recovery after subtotal resection is proliferation of hepatocytes.

The mechanisms of proangiogenic activity of multipotent stromal cells from human umbilical cord were analyzed in vitro. The absence of secreted forms of proangiogenic growth factor VEGF-A in the culture medium conditioned by umbilical cord-derived multipotent stromal cells was shown by ELISA. However, the possibility of paracrine stimulation of cell proliferation, mobility, and directed migration of endothelial EA.hy926 cells was demonstrated by using MTT test, Transwell system, and monolayer wound modeling. The capacity of multipotent stromal cells to acquire the phenotype of endothelium-like cells was analyzed using differentiation media of three types. It was found that VEGF-A is an essential but not sufficient inductor of differentiation of umbilical cord-derived multipotent stromal cells into CD31+ cells.

Mesenchymal stromal/stem cells derived from human umbilical cord (UC-MSCs) uniquely combine properties of embryonic and postnatal MSCs and may be the most acceptable, safe, and effective source for allogeneic cell therapy e.g. for therapeutic angiogenesis. In this report we describe pro-angiogenic properties of UC-MSCs as manifested in vitro. UC-MSCs were isolated from human Wharton's jelly by enzymatic digestion. Presence of soluble forms of VEGF-A in UC-MSC-conditioned media was measured by ELISA. Effects of the conditioned media on human umbilical vein-derived endothelial EA.hy926 cells proliferation were measured by MTT-assay; changes in cell motility and directed migration were assessed by scratch wound healing and transwell chamber migration assays. Angiogenesis was modeled in vitro as tube formation on basement membrane matrix. Progressive differentiation of MSCs to endothelioid progeny was assessed by CD31 immunostaining. Although no detectable quantities of soluble VEGF-A were produced by UC-MSCs, the culture medium, conditioned by the UC-MSCs, effectively stimulated proliferation, motility, and directed migration of EA.hy926 cells. In 2D culture, UC-MSCs were able to acquire CD31(+) endothelial cell-like phenotype when stimulated by EA.hy926-conditioned media supplemented with VEGF-A165. UC-MSCs were capable of forming unstable 2D tubular networks either by themselves or in combinations with EA.hy926 cells. Active spontaneous sprouting from cell clusters, resulting from disassembling of such networks, was observed only in the mixed cultures, not in pure UC-MSC cultures. In 3D mode of sprouting experimentation, structural support of newly formed capillary-like structures was provided by UC-MSCs that acquired the CD31(+) phenotype in the absence of exogenous VEGF-A. These data suggest that a VEGF-A-independent paracrine mechanism and at least partially VEGF-A-independent differentiation mechanism are involved in the pro-angiogenic activity of UC-MSCs.