Acute portal hypertension reflecting shear stress as a trigger of liver regeneration following partial hepatectomy

The concept of injury in liver regeneration after partial hepatectomy (PHx), and the reason hepatocytes that have not been directly injured regenerate, remain unclear. It is known that shear stress resulting from blood flow plays an important role in the mechanism of remodeling blood vessels, and portal pressure reflects shear stress. This study was conducted to determine whether acute portal hypertension (APH) can become a trigger of liver regeneration as shear stress following PHx in a rat model. Portal pressures became elevated immediately after 70% and 90% PHx, peaking on postoperative day (POD) 3, and thereafter decreasing in proportion to the diminution of liver regeneration. The portal pressures after 90% PHx were significantly higher than those after 70% PHx even on POD 7, while those of the portocaval (PC) shunt groups decreased following PC shunting both with and without 70% PHx. The liver/body weight (LW/BW) ratio also decreased in the PC shunt both with and even without 70% PHx. The gradient expressions of class I antigen on sinusoidal endothelial cells (SEC) were found only in the periportal area, which has the highest portal pressure in the healthy rat liver. However, after hepatectomy these expressions were detected from the periportal area to the central venous area. These results suggest that APH as shear stress following PHx may not only become a trigger of hepatocyte regeneration, but also of SEC regeneration, and that surplus APH induces liver dysfunction.     

DNA polymerases and Ki-67 nuclear antigen are induced in correlation with the resected mass of rat liver up to 90%

Background and aims: We studied the regeneration potential by measuring induction of DNA polymerases in the remnant rat liver after a partial hepatectomy (PHx) that is maximal but compatible with survival. Methods: The regenerating rat liver was obtained after the 90% PHx. The induction of activities of DNA polymerase α, δ, and ɛ were measured after partial purification. The Ki-67 nuclear antigen was also detected histochemically. These parameters were compared with those after both 30% and 70% PHx. Results: The 90% hepatectomy resulted in the strong inductions of DNA polymerase α, δ, and ɛ, at 48 h after operation, in association with increases in wet weight and total DNA in the remnant liver. The enzyme induction was much higher after 90% PHx than after 30% and 70% hepatectomy, in correlation with the resection volume. At 48 h after 90% hepatectomy, the Ki-67 positive cells increased up to 47.2% of hepatocytes in the remnant liver. Conclusion: The higher induction of replication enzymes by 90% hepatectomy reflects more cells entering mitogenic cell cycle, which supports the fast regeneration of the remnant liver. The number of proliferating hepatocytes is stringently controlled by an unknown mechanism sensing the mass of resected liver parenchyma. Received: 9 March 1999; In revised form: 2 August 1999 Accepted: 20 August 1999     

Immediate increase of portal pressure, reflecting sinusoidal shear stress, induced liver regeneration after partial hepatectomy

The mechanisms whereby hepatocytes in the normal liver can be primed for replication following partial hepatectomy (PHx) are poorly understood. To determine whether "shear stress," which is induced by acute portal hypertension after PHx, is involved in liver regeneration, we studied liver regeneration in rats with splenic transposition (SPT) in which we can minimize the postoperative elevation of portal pressure. Rats underwent 70% PHx following splenic transposition or sham surgery and were killed at various time points to measure portal pressure and other factors. In the control groups, the portal pressure was significantly increased immediately after surgery, peaking at 48 h, and returning to near the preoperative levels by 168 h after PHx. In the SPT group, although portal pressure increased immediately, it decreased to the control levels 6 h after PHx and thereafter repeatedly increased. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels peaked at 24 and 6 h after PHx, respectively. Proliferative cell analysis was done using MIB-5 antibody, and there were no significant differences between the two groups. Furthermore, liver weight was restored in the same way in both groups. Taken together, the results suggest that an immediate increase in portal pressure is necessary for the initiation of liver regeneration. Received for publication on Jan. 20, 1999; accepted on Feb. 25, 1999     

切应力对大鼠肝窦内皮细胞分泌功能的影响

目的了解不同切应力下肝窦内皮细胞分泌肝细胞生长因子（HGF）、白细胞介素-6（IL-6）、-氧化氮（N0）及-氧化氮合成酶（NOS）的分泌量，探讨切应力对原代培养的大鼠肝窦内皮细胞分泌功能的影响。方法构建血流动力学模型。实验分为对照组（切应力为0 dyn／cm^2）和实验组2组。实验组又按切应力不同分为12、24和48dyn／cm^2 3个亚组。每组分别在4、8、12及24h抽取1ml培养基，利用试剂盒检测培养基中HGF、IL-6、NO和NOS浓度。结果在不同切应力下，肝窦内皮细胞分泌HGF、IL-6、NO和NOS各不相同，在同一时相随着切应力的升高。HGF、IL-6、NO和NOS的分泌量也升高，实验组明显高于对照组（P〈0．01），且48dyn／cm^2组明显高于另两个亚组（P〈0．01）；实验组作用8、12、24h时，HGF、IL-6、No及NOS分泌量明显高于作用4h时。结论体外实验证实，切应力升高时肝窦内皮细胞分泌HGF、IL-6、NO和NOS的量明显增加，提示部分肝切除术后门静脉压力急剧升高能促使肝窦内皮细胞活化。分泌大量促肝细胞再生的细胞因子和介质。     

Anti-transforming growth factor-β1 antibody transiently enhances DNA synthesis during liver regeneration after partial hepatectomy in rats

The regulation of liver regeneration after partial hepatectomy (PHx) is complex and involves many different cytokines. We investigated the role of one of these, transforming growth factor-β1 (TGF-β1), an inhibitor of liver regeneration, in a Wistar male rat model, in which anti-TGF-β1 antibody was injected immediately or 24 h after 70% PHx. Livers from treated animals contained an increased number of cells in S phase, according to 5-bromo-2′-deoxyuridine (BrdU) labeling 36 h after PHx. Antibody administration 24 h after PHx resulted in the highest peak of proliferation; moreover, peak MIB-5 labeling was also observed at that time. However, neither residual liver-weight-to-body-weight ratios nor regeneration rates differed significantly between any of the animals. Therefore, we also measured levels of serum TGF-β1 and hepatocyte growth factor (HGF; an activator). With antibody administration at 0 or 24 h, TGF-β1 levels were diminished at 24 or 36 h as compared with levels in control rats, but then rebounded, reaching a delayed peak at 48 or 72 h after PHx, respectively. Interestingly, there were also similar trends in HGF levels. These results indicate that TGF-β1 may inhibit the G1 checkpoint, and serum TGF-β1 concentration may influence HGF to regulate liver regeneration and to maintain homeostasis of proliferation after PHx. Received: November 15, 2000 / Accepted: February 15, 2001     

Plasminogen mediates liver regeneration and angiogenesis after experimental partial hepatectomy

BACKGROUND: Plasmin system components are upregulated after partial hepatectomy, but their contribution to surgery-induced hepatic angiogenesis and regeneration is unclear. Liver regeneration and angiogenesis after partial hepatectomy were examined in mice lacking plasminogen or urokinase plasminogen activator (uPA). METHODS: Mice with a single-gene deletion of plasminogen or uPA were subjected to 70 per cent partial hepatectomy. Liver regeneration was measured as relative liver weight and cell proliferation index. Angiogenesis was quantified by determining hepatic microvessel density after staining for sinusoidal endothelial cells. RESULTS: The liver remnant weight was significantly reduced in mice lacking plasminogen or uPA compared with that in wild-type mice on days 2 and 7 after partial hepatectomy. This correlated with impaired cell proliferation. In wild-type mice, regeneration was accompanied by a significant increase in microvessel density after hepatectomy; this increase was impaired in plasminogen-deficient mice. CONCLUSION: Plasminogen and uPA are essential for optimal liver regeneration. In addition, plasminogen appears to be a major determinant in regeneration-associated hepatic angiogenesis.     

A Distinct Subpopulation of Bone Marrow Mesenchymal Stem Cells,Muse Cells,Directly Commit to the Replacement of Liver Components

Genotyping graft livers by short tandem repeats after human living‐donor liver transplantation (n = 20) revealed the presence of recipient or chimeric genotype cases in hepatocytes (6 of 17, 35.3%), sinusoidal cells (18 of 18, 100%), cholangiocytes (15 of 17, 88.2%) and cells in the periportal areas (7 of 8, 87.5%), suggesting extrahepatic cell involvement in liver regeneration. Regarding extrahepatic origin, bone marrow mesenchymal stem cells (BM‐MSCs) have been suggested to contribute to liver regeneration but compose a heterogeneous population. We focused on a more specific subpopulation (1–2% of BM‐MSCs), called multilineage‐differentiating stress‐enduring (Muse) cells, for their ability to differentiate into liver‐lineage cells and repair tissue. We generated a physical partial hepatectomy model in immunodeficient mice and injected green fluorescent protein (GFP)‐labeled human BM‐MSC Muse cells intravenously (n = 20). Immunohistochemistry, fluorescence in situ hybridization and species‐specific polymerase chain reaction revealed that they integrated into regenerating areas and expressed liver progenitor markers during the early phase and then differentiated spontaneously into major liver components, including hepatocytes (≈74.3% of GFP‐positive integrated Muse cells), cholangiocytes (≈17.7%), sinusoidal endothelial cells (≈2.0%), and Kupffer cells (≈6.0%). In contrast, the remaining cells in the BM‐MSCs were not detected in the liver for up to 4 weeks. These results suggest that Muse cells are the predominant population of BM‐MSCs that are capable of replacing major liver components during liver regeneration.     

Effects of ischemic preconditioning on regenerative capacity of hepatocyte in the ischemically damaged rat livers

BACKGROUND: Liver regeneration after partial hepatectomy is regulated by several factors that activate or inhibit hepatocyte proliferation. A short period of ischemia-reperfusion (IR), called ischemic preconditioning (IPC), protects the liver against subsequent sustained ischemic insults. The present study investigated the effects of IPC on liver regeneration after partial hepatectomy under IR in rats. MATERIALS AND METHODS: Male Wistar rats were subjected to 45 min of total hepatic ischemia, and 70% hepatectomy was performed just before reperfusion. Animals were pre-treated with either IPC (10/15 min) (IPC + PHx group) or not (ischemia + PHx). The survival rate, serum transaminases, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 levels, hepatocyte proliferation and histological change of the remnant liver were measured in both groups and compared with non-ischemic controls subjected to 70% hepatectomy alone (PHx group). RESULTS: The survival rate was significantly better in the IPC + PHx group than in the ischemia + PHx group. Furthermore, IPC reduced liver injury determined by liver histology and serum transaminases. There was an early rise in serum TNF-alpha and IL-6 levels in the ischemia + PHx group. Compared with non-ischemic controls, IPC significantly decreased TNF-alpha, but not IL-6 during the late (24 and 48 h) phases of reperfusion. Rats subjected to 70% hepatectomy and 45 min of hepatic ischemia showed significantly reduced hepatocyte proliferation (mitotic index, proliferating cell nuclear antigen, and relative liver weight) when compared with animals subjected to hepatectomy alone. However, hepatocyte proliferation was markedly increased in rats pretreatment with IPC when compared with ischemic controls. CONCLUSION: These results suggest that ischemic pre-conditioning ameliorates the hepatic injury associated with ischemia-reperfusion and has a stimulatory effect on liver cell regeneration that may make it valuable as a hepatoprotective modality. Il-6 appears to be key mediator in promoting regeneration after combined ischemia and hepatic resection.     

The promotion of liver regeneration in mice after a partial hepatectomy as a result of the modulation of macrophage activation by dexmedetomidine

BackgroundThis study investigates the effect of dexmedetomidine (DEX), a highly selective agonist of alpha 2-adrenergic receptors (α2-ARs), on the regulation of hepatic macrophage activation in liver regeneration.MethodsA two-thirds partial hepatectomy (PHx) mouse model was performed. DEX (25 μg/kg) or a vehicle control (saline) was injected i.p. at 30 min before and every 12 h after PHx. The expression of α2B-ARs in the liver was detected using immunofluorescence staining. The effects of DEX on liver regeneration were assessed by Ki67 staining. The gene expression of inflammatory cytokines in isolated hepatic macrophages was quantified 36 h after the PHx.Resultsα2B-ARs colocalized with hepatic macrophages after the PHx. The number of Ki67-positive hepatocytes in the mice treated with DEX was markedly increased (p < 0.05). The increases in Ki67-positive hepatocytes after treatment with DEX were inhibited in the macrophage-depleted mice. DEX treatment inhibited the expression of major pro-inflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor and elevated the expression of anti-inflammatory cytokines IL-4, IL-10, and transforming growth factor-β1 in hepatic macrophages 36 h after the PHx (p < 0.05).ConclusionsThe α2B-AR subtype is expressed in hepatic macrophages after a PHx. DEX modulates hepatic macrophage activation toward an anti-inflammatory phenotype via α2B-AR, which promotes the process of liver regeneration.     

Preventive Effect of Fibroblast Growth Factor and Hepatocyte Growth Factor on Ceramide‐Induced Dysfunction Human Small Intestinal Cells

Aim:  To investigate whether TNF‐ is necessary for hepatocyte proliferation, we study liver regeneration after partial hepatectomy in mice lacking TNF receptor‐1.
Methods:  TNF receptor type‐1 knockout mice and wild‐type mice were subjected to two‐thirds partial hepatectomy (PHx). Liver regeneration was evaluated by assessing liver weights and Ki67 immunohistochemistry. Riken cDNA microarray analysis was performed on liver samples from mice undergoing PHx to compare clearly differentiated mouse PHx models (TNFR‐1 knockout mice‐K group, and wild type mice‐W group).
Results:  The cumulative survival after PHx in K group was lower than in W group. The mortality rate in K group during the first 3 days after PHx was higher (33%) than in W group. The time to regain the liver weight in K group was 14 days and 7 days in W group. The plasma IL‐6 levels in K type at 3 hr was significantly higher than in W group. The Ki67 expression in K group at 4 days was lower than in W group. LPS, Toll like receptor 4 precursor and MAPK 8 interacting protein in K group was higher than in W group. For cell cycle‐regulated genes, cyclin D1, NFB light chain and TNF receptor super family membrane 1a in K group was lower than in W group.
Conclusions:  Lack of TNF‐ signaling through TNF receptor type 1 suppresses liver regeneration after partial hepatectomy in spite of enhancement of LPS–JNK pathway, no TNF‐a and IL‐6 pathway.     

Mechanism of postoperative liver failure after excessive hepatectomy investigated using a cDNA microarray

Background/Purpose: Excessive hepatectomy often causes fatal liver failure. We have reported that this is mainly mediated by apoptosis, characterized pathologically by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) assay-positive hepatocytes and a ladder pattern in DNA fragmentation assays. Methods: To investigate the mechanism, we used cDNA microarray analysis to compare clearly differentiated rat partial hepatectomy (PHx) models (90%PHx, and 95%PHx). All 90%PHx rats survived, but the 95%PHx animals died of hepatic failure within 96 h. Remnant liver was obtained at four time points (1, 3, 12, and 24 h after PHx). After RNA extraction, two samples were labeled with different fluorescent dyes and hybridized to the Institute of Physical and Chemical Research (RIKEN) set of 18 816 full-length enriched mouse cDNA arrays. Scanning for fluorescent dye signals was performed, and the mRNA expression ratio of the two models was examined. Results: Genes of the p21 cyclin-dependent kinase (CDK) inhibitor, Fas, interleukin (IL)-18, and many caspases were upregulated at 1 h after PHx in the 95%PHx group. On the other hand, genes of Bcl-2, heat shock proteins, and glutathione-S-transferase were downregulated. Conclusions: We concluded that fatal hepatic failure after excessive hepatectomy was characterized by increased apoptosis and diminished liver regeneration. Received: July 25, 2001 / Accepted: November 16, 2001     

Kupffer cell tumor necrosis factor-alpha production is suppressed during liver regeneration

Mammalian liver regeneration following resection invokes intrinsic hepatic responses which result in rapid tissue repair. The role of soluble immune cytokines in this phenomenon is not known. The capacity of Kupffer cells (KC) from regenerating liver to produce the potent cytokine TNF-alpha was evaluated. Twenty-four hours after 70% partial hepatectomy (PHx) or sham operation, Kupffer cells were harvested from collagenase-digested Wistar-Furth rat livers and purified (greater than 95% by phagocytosis) by adherence. Following overnight culture with or without the cyclooxygenase inhibitor indomethacin (10 microM), 5 x 10(5) KC were repleted with fresh media with or without 2.5 micrograms/ml lipopolysaccharide (LPS). Supernatant TNF-alpha activities (units/ml) were measured using the L929 fibroblast lysis assay. With LPS, sham KC TNF-alpha levels were significantly higher (P less than 0.001) than those for PHx KC. Indomethacin significantly increased PHx KC TNF-alpha levels, but did not affect those for sham KC, suggesting autoregulation by arachidonic acid cyclooxygenase metabolites following PHx. We conclude that KC TNF-alpha production is suppressed following PHx by a mechanism apparently regulated by eicosanoid metabolism. During the stress of hepatic regeneration, a coordinated limitation of excessive TNF-alpha responses by PHx liver KC may naturally protect the host.     

血晶素对大鼠70%肝脏切除后再生的影响

目的 探讨血晶素(Hemin)对大鼠70%肝脏切除术后肝脏再生的影响.方法 复制大鼠70%肝脏切除模型,随机分成血晶素治疗组和生理盐水对照组,在术后第1天、第2天、第3天和第7天测定比较肝重/体重、血清肿瘤坏死因子α(TNF-α)、肝脏组织中血晶素加氧酶1(HO-1)含量及肝细胞核增殖蛋白抗原(PCNA)表达指数.结果 术后第7天治疗组肝重/体重明显高于对照组(P<0.05),第3天开始肝细胞 PCNA表达指数较对照组升高,差异有统计学意义(P<0.01).治疗组术后肝脏组织中HO-1浓度比对照组高,血清TNF-α的含量比对照组低(P<0.05).结论 血晶素大鼠肝脏70%切除术后肝脏再生的速度明显提高,这可能跟HO-1表达升高有关.     

Effects of Ozone Oxidative Preconditioning on Liver Regeneration after Partial Hepatectomy in Rats

ABSTRACT

Aim: Similar protective effect of ischemic and ozone oxidative preconditioning (OzoneOP) in hepatic ischemia–reperfusion (I/R) injury was demonstrated, providing evidences that both preconditioning settings shared similar biochemical mechanisms of protection. We investigated the effects of OzoneOP on liver regeneration after 70% partial hepatectomy (PHx) in rats. Methods: Rats were divided into three groups: PHx, I/R + PHx, and OzoneOP + I/R + PHx groups. Ozone (intraperitoneal, 1.2 mg/kg) was given to rats subjected to I/R and 70% hepatectomy daily five times before operation. At 24 hr and 48 hr after resection, samples were collected for the measurement of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6). Moreover, liver regeneration rate, proliferating cell nuclear antigen (PCNA) labeling index, mitotic index, and histopathological examination were evaluated. Results: OzoneOP reduced liver injury determined by liver histology and serum transaminases. There was a rise in serum TNF-α and IL-6 levels in the I/R + PHx group whereas OzoneOP significantly decreased the rise in the level of TNF-α but not IL-6 on the 24 hr and 48 hr of reperfusion. Moreover, liver regeneration in OzoneOP + PHx group, as assessed by the regenerated liver weight, mitotic, and PCNA-labeling index, was significantly improved when compared to I/R + PHx group. Conclusion: These results suggest that OzoneOP ameliorates the hepatic injury associated with I/R and has a stimulatory effect on liver cell regeneration that may make it valuable as a hepatoprotective modality.     

BCL-2 and BAX expression and cell proliferation,after partial hepatectomy with and without ischemia,on cholestatic liver in rats: an experimental study

BACKGROUND: Liver regeneration after partial hepatectomy (PHx) is regulated by several factors that activate or inhibit hepatocyte proliferation. Apoptosis seems to play an important role in cellular proliferation and liver regeneration. This study investigates the expression apoptosis-associated genes bcl-2 and bax, and the presence of apoptosis and cell proliferation after PHx, in normal and jaundiced rats with or without superimposed ischemia. MATERIALS AND METHODS: The study included 50 male Wistar rats assigned into; five groups (10 rats each). On day 0, rats of groups II, IV, and V underwent common bile duct ligation (BDL). On day 10, total liver ischemia (TLI) (occlusion of hepatic artery and portal vein-TLI) for 30 min was performed on animals of group V. When TLI was completed, all 30 animals (of groups I, IV, and V) underwent PHx (68%). Animals of group III underwent only TLI for 30 min. Rats of groups I, IV, and V were sacrificed 24 and 48 h after PHx was completed. Rats of group II were sacrificed 10, 11, and 12 days after BDL. Rats of group III were sacrificed immediately, 24 and 48 h after TLI completion. Liver tissue was obtained and pathologic examination included: (a) H&E stain, (b) in situ hybridization (detection of bcl-2 and bax mRNA) in paraffin sections, (c) Western blot analysis for the evaluation of bcl-2 and bax protein levels, (d) in situ hybridization (TUNEL) for the detection of apoptotic bodies, and (e) immunohistochemical stains (streptavidin-biotin method) in paraffin sections to detect cells that (i) express bcl-2 and bax proteins and (ii) undergo proliferation (Ki67+ cells). Results were expressed following morphometric analysis. RESULTS: Before hepatectomy, bcl-2 (protein or mRNA) levels were higher in jaundiced rats vs controls. Furthermore, bax (protein or mRNA) levels and apoptotic body index (ABI) were higher in cholestatic livers. After hepatectomy, there was an early decrease in the protein and mRNA levels of antiapoptotic gene bcl-2 and a late increase of proapoptotic gene bax and the ABI, compared to controls. Cell proliferation of hepatocytes was lower in group V (BDL + TLI) compared to that of groups II and IV (BDL). CONCLUSIONS: This study shows that apoptosis takes place in cholestatic livers with or without superimposed ischemia and may contribute in the impaired regenerative response observed in livers of jaundiced rats after partial hepatectomy.     

TGF-β1在肝再生调控中的作用研究

目的 探讨70%肝部分切除后TGF-β1在肝再生调控中的作用.方法 MTT方法 检测TGF-β1对原代肝细胞的作用;建立70%肝部分切除(PH)模型,收集切除后2d的血清,用MTT方法 检测其对IG12细胞的促增殖作用,并用免疫细胞化学方法 观察其对IG12细胞TGFβ1表达的影响;用免疫组织化学和Western blot检测再生肝组织中TGF-β1的表达.结果 TGF-β1能抑制原代肝细胞增殖;PH后大鼠血清不仅对IG12细胞有明显的促增殖作用,还能提高IG12细胞TGF-β1的表达;免疫组化结果 显示大鼠PH后肝细胞TGF-β1表达逐渐下降,至第3天呈阴性结果 ,而后升高,直至再生结束时稳定在正常肝脏表达水平,Western blot显示PH后再生早期TGF-β1表达暂时升高,12 h达到高峰,第1天开始下降,第3天降至最低点,5d开始逐渐升高,至第7天恢复到正常水平.结论 TGF-β1明显抑制肝细胞增殖,在PH后肝再生过程中,肝组织中TGF-β1表达明显下降,有助于肝再生的完成.     

Blood transfusion causes deterioration in liver regeneration after partial hepatectomy in rats.

BACKGROUND: This study investigated the effects of blood transfusion on liver regeneration and function after hepatectomy in rats. METHODS: Inbred male Sprague-Dawley rats underwent a sham operation or a 70% hepatectomy (PHx) and were randomly divided into seven groups according to transfusion type: groups I and II underwent a sham operation and received saline (I) or whole blood (II). Groups III to VII underwent PHx with saline (III), whole blood (IV), irradiated/leukocyte-depleted whole blood (V), plasma (VI), or autologous blood (VII). The liver regeneration rate, proliferating cell nuclear antigen (PCNA) labeling index, serum aspartate aminotransferase, alanine aminotransferase, purine nucleoside phosphorylase (PNP) activity, hepatocyte growth factor (HGF), and activated transforming growth factor beta1 (TGF-beta(1)) were measured 6 and 24 h and 5 days after PHx. RESULTS: The liver regeneration rate and PCNA labeling index were lower in groups IV and V than in the other groups. Serum liver enzymes 6 h after PHx were worst in groups IV and V. PNP activity increased most in group IV, 6 and 24 h after PHx. The HGF values 6 h after PHx in all the transfused groups were lower than in group III. The activated TGF-beta(1) level 6 h after surgery was highest in group IV. CONCLUSION: Whole blood or irradiated/leukocyte-depleted whole blood impaired liver regeneration after PHx, probably through the production of activated TGF-beta(1) and HGF outside the liver, and plasma or autologous blood reduced the deleterious effects.     

Novel therapy for liver regeneration by increasing the number of platelets

Platelets are the smallest blood constitutes which contain three types of granules; alpha granules, dense granules, and lysosomal granules. Each granule contains various biophysiological substances such as growth factors, cytokines, etc. Platelets have been conventionally viewed as a trigger of inflammatory responses and injury in the liver. Some studies revealed that platelets have strong effects on promoting liver regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and describes three different mechanisms involved; (1) the direct effect on hepatocytes, where platelets translocate to the space of Disse and release growth factors through direct contact with hepatocytes, (2) the cooperative effect with liver sinusoidal endothelial cells, where the dense concentration of sphingosine-1-phosphate in platelets induces excretion of interleukin-6 from liver sinusoidal endothelial cells, and (3) the collaborative effect with Kupffer cells, where the functions of Kupffer cells are enhanced by platelets.     

Endothelial progenitor cells contribute to accelerated liver regeneration

Two classes of circulating endothelial cells (CECs) have been identified and are distinguished by the expression of the stem cell markers CD117 or CD133 together with endothelial-specific antigens. Stem cell marker-positive CECs originate from bone marrow and have been designated as circulating endothelial progenitors (CEPs). We have demonstrated that exogenous vascular endothelial growth factor (VEGF) effectively mobilizes CEP cells. Furthermore, it has been demonstrated that VEGF regulates liver regeneration after partial hepatectomy. Although local endothelial cells can regulate tissue mass during liver regeneration, the contribution of CEPs to this process is unknown. We discovered loss of CD117 and CD133 from murine CEP cells and that both markers underestimated the number of bone marrow-derived CEP cells. We therefore used wild type and green fluorescent protein (GFP)-bone marrow transplanted into wild-type mice and performed 70% hepatectomies. Furthermore, we found that treatment with exogenous VEGF accelerated liver regeneration after 70% hepatectomy, whereas immunohistochemical analysis showed a 7-fold increase in the incorporation of CEP cells into liver vasculature. These results suggest that CEP cells play a role in regulating liver regeneration and that VEGF treatment can mobilize CEP cells to accelerate this process.