Role of transforming growth factor-beta1 (TGF-beta1) in endotoxin-induced hepatic failure after extensive hepatectomy in rats

Postoperative infections after hepatectomy sometimes lead to fatal hepatic failure, but the mechanism of the hepatic failure is unclear. Wistar rats underwent 90% hepatectomy, and were then divided into three groups: (i) the SAL group, injected with normal saline; (ii) the LPS group, injected with lipopolysaccharide (LPS) every day for 1 week; and (iii) the LPS plus TGF-Ab (LPS+TGF-Ab) group, injected with LPS with anti-transforming growth factor-beta1 (TGF-beta1) antibody. We investigated survival rates, TGF-beta1 expression in the liver, liver regeneration by proliferating cell nuclear antigen labeling index, hepatocyte apoptosis by single stranded DNA labeling index, and perisinusoidal fibrosis using Masson's trichrome staining. The LPS group (30.4%) had a significantly lower survival rate than the SAL group (84%) and tended to be lower than the LPS+TGF-Ab group (49.4%). Liver regeneration in the LPS group was significantly lower than in the other groups. In the LPS group, hepatocyte apoptosis and perisinusoidal fibrosis was significantly more remarkable, and TGF-beta1 expression was significantly higher than in the SAL group. TGF-beta1 enhanced by LPS plays an important role in the mechanism of hepatic failure by infections after hepatectomy, especially in inhibition of liver regeneration, and induction of hepatocyte apoptosis and perisinusoidal fibrosis.     

Transforming growth factor-beta is activated by plasmin and inhibits smooth muscle cell death in human saphenous vein

BACKGROUND: The effect of activation of endogenous transforming growth factor-beta (TGF-beta) on smooth muscle cell apoptosis was assessed in human saphenous vein. METHODS: Segments of human saphenous vein, obtained at the time of bypass graft surgery, were cultured for 14 days. During this time, smooth muscle cells accumulated in the intima as a result of proliferation and migration, partly counterbalanced by apoptotic cell death. RESULTS: Addition of exogenous TGF-beta(1) had no effect on smooth muscle cell proliferation or apoptosis. However, antibody neutralization of endogenous TGF-beta(1) caused significant increases in smooth muscle cell death in the media and intima without any change in proliferation. A plasmin inhibitor (alpha-N-acetyl-L-lysine methyl ester), a specific urokinase-type plasminogen activator (uPA) inhibitor (amiloride) and an anti-catalytic anti-uPA antibody all caused decreases in the tissue content of active TGF-beta and increases in smooth muscle cell death in the media and intima. CONCLUSIONS: These data suggest that the amount of TGF-beta in human saphenous vein is sufficient, when in the active form, to protect smooth muscle cells against apoptosis. Adding exogenous TGF-beta(1) has no beneficial effect, but decreasing the amount of active TGF-beta causes smooth muscle cells to undergo apoptosis. Plasmin, generated by uPA, appears to be an important activator of endogenous latent TGF-beta.     

Regional and general effects of hepatic lobes with impaired blood flow after hepatic resection

BACKGROUND/AIMS: In hepatic surgery, blood flow to some parts of the liver may become impaired. At present, no consensus has been reached on ways to treat such affected parts of the liver with impaired blood supply. METHODOLOGY: After the ligation of branches of rat's hepatic artery and/or portal vein, the ligated and non-ligated lobes were studied at fixed intervals up to 84 days. Parameters include hepatic tissue blood flow assessed by a laser Doppler flowmeter, liver regeneration ability using bromodeoxyuridine, apoptosis using anti-single-stranded DNA Ig-G antibody, and vulnerability to an endotoxic injection. RESULTS: Hepatic artery ligation group showed no obvious changes in either the ligated or non-ligated lobes, and these lobes had no effects on the whole body. Of the portal vein ligation group, although the ligated lobes underwent marked atrophy, the compensatory hypertrophy of the non-ligated lobes took place sufficiently and no life-threatening conditions were observed. With regard to the hepatic artery/portal vein ligation (HA/PVL) group, hepatic blood flow in the ligated lobes rapidly decreased, and all hepatocytes underwent necrosis 1 day after surgery. In the non-ligated lobes, however, significant increases in the bromodeoxyuridine labeling index were detected at 1, 2, and 3 days after surgery, and compensatory hypertrophy was recognized. Indocyanine green 15-minute retention rate rapidly increased 1 day after surgery, and there were significant differences compared to the sham group up to 7 days after surgery. The postsurgical mortality rate in the HA/PVL group was significantly high at 13%, and mortality rate following endotoxin injection was as high as 75%. CONCLUSIONS: Affected parts of the liver with blockage of both the hepatic artery and portal vein should be resected.     

Long-term effect of hepatocyte transplantation on fulminant hepatic failure in rats

BACKGROUND/AIMS: Effect of hepatocyte transplantation on long-term survival after fulminant hepatic failure was studied in rats. METHODOLOGY: Sprague-Dawley rats were divided into: Group I (n = 65), intrasplenic hepatocyte transplantation followed by fulminant hepatic failure; Group II (n = 31), intrasplenic saline injection followed by fulminant hepatic failure; Group III (n = 24), 70% hepatectomy. For survival, 35 animals of Group I and 19 of Group II were observed. Six animals of each group were euthanized on postoperative days 1, 7, 14 and 28 to study biochemistry, liver growth rate, labeling index of proliferating cell nuclear antigen, hepatocyte growth factor and transforming growth factor. RESULTS: Postoperatively, Group I had a better survival than Group II. Group I also showed a better biochemical profile on day 1 as compared with Group II, and on day 28, Group I had a normal profile. On day 28, the remnant liver in Group I reached 97% of the original liver weight. Group I had a better proliferating cell nuclear antigen labeling index than Group II on day 1 and exceeded Group III on day 14. On day 1, Group I had lower levels of hepatocyte growth factor and transforming growth factor than Group II while hepatocyte growth factor on days 7, 14 and 28 showed no difference between Group I and Group III. CONCLUSIONS: Hepatocyte transplantation has achieved a long-term survival and improved the liver regeneration in rats with fulminant hepatic failure.     

囊型肝包虫囊周肝细胞"消失"机制的初步研究

目的 观察囊型肝包虫周围肝细胞的病理形态学变化（肝细胞萎缩、坏死、凋亡）,初步探讨囊型肝包虫病肝细胞“消失”机制。方法 对30例肝包虫囊肿周围肝组织通过光镜观察肝组织的病理形态学变化,运用TUNEL法测定肝细胞凋亡,采用免疫组化技术检测肝包虫囊肿周围肝组织及正常肝组织中Bcl—2及Bax蛋白的表达。结果 TUNEL检测囊型肝包虫病患者肝细胞凋亡指数（TI）为0．12％,与正常肝组织（TI=O．16％）比较差异无显著性（P〉0．05）;Bc卜2及Bax蛋白的囊周肝组织呈低表达,分别为6．67％和13．33％,正常肝组织Bcl一2和Bax均为10．00％,差异无显著性（P〉O＋05）。病理组织学观察示肝细胞萎缩,肝细胞坏死明显。结论 肝细胞萎缩、坏死可能是引起肝细胞“消失”的主要机制,肝细胞压迫性和营养不良性萎缩、肝细胞坏死、肝细胞凋亡共同参与囊型肝包虫病肝细胞“消失”过程。     

Role of the spleen in liver fibrosis in rats may be mediated by transforming growth factor beta-1

BACKGROUND: The effect of the spleen on the cirrhotic liver is unknown. Transforming growth factor-beta 1 (TGF-beta 1), which plays a crucial role in the matrix production during liver fibrosis, is an inhibitory factor regarding the regeneration of hepatocytes. In this study, we investigated the TGF-beta 1 production in the spleen of cirrhotic rats and the effects of a splenectomy on the healing process from liver fibrosis. METHODS: Thirty-six Wistar male rats were used. Thioacetamide (TAA) was administered intraperitoneally for 24 weeks. The rats underwent either a sham operation (TAA + Sham) or a splenectomy (TAA + SPL). The improvements in liver fibrosis and liver regeneration were investigated 10, 30 and 60 days after the operations in each group. The effect of a splenectomy on the plasma concentration of TGF-beta 1 in the portal vein was investigated by ELISA. The TGF-beta 1 expressions in the spleen were measured using immunohistochemical staining and the degree of such expression was measured using RT-PCR. The activity of TGF-beta 1 in the portal vein of TAA + Sham and TAA + SPL was assessed by the inhibiting effect of rat parenchymal hepatocyte proliferation in primary culture. RESULTS: Liver regeneration (PCNA-labeling index) in the TAA + SPL rats was stimulated more at 10 and 30 days after the operation (P < 0.05) than in the TAA + Sham rats, and the improvement of liver fibrosis (fibrosis rate) in the TAA + SPL rats was higher at 60 days (P < 0.05) than in the TAA + Sham rats. The plasma concentration of TGF-beta1 of the portal vein in TAA + SPL rats was significantly lower than in the TAA + Sham rats for each period. Immunohistochemically, TGF-beta1-positive stained cells were recognized in the spleen macrophages in the red pulp of cirrhotic rats. The plasma of the TAA + Sham rats at 10 and 30 days after the operation was significantly stronger than that of the TAA + SPL rats in inhibiting the proliferation of rat hepatocytes of primary culture. Inhibitory effects were then dose-dependently neutralized by monoclonal TGF-beta 1 antibody. CONCLUSION: Spleen-derived TGF-beta 1 may thus play an inhibitory role in the healing of liver cirrhosis by inhibiting the regeneration of the damaged liver.     

TGF-beta/Smad signaling in the injured liver

TGF-beta, acting both directly and indirectly, represents a central mediator of fibrogenic remodeling processes in the liver. Besides hepatic stellate cells (HSCs), which are induced by TGF-beta to transdifferentiate to myofibroblasts and to produce extracellular matrix, hepatocytes are also strongly responsive for this cytokine, which induces apoptosis during fibrogenesis and provides growth control in regeneration processes. Based on this, TGF-beta-mediated hepatic responses to injury are the result of a complex interplay between the different liver cell types. In this review we summarize the knowledge about TGF-beta signal transduction in HSCs with special impact on Smad pathways. We further describe a molecular cross-talk between profibrogenic TGF-beta and antifibrogenic IFN-gamma signaling in liver cells. Finally, we introduce hepatocyte plasticity and epithelial-to-mesenchymal transition in the liver, which is well established in tumorigenesis, as a potential feature of fibrogenesis and highlight possible action points of TGF-beta in these contexts.     

Portal serum human hepatocyte growth factor levels after partial hepatectomy.

BACKGROUND/AIMS: We investigated whether or not hepatocyte growth factor increases in portal serum via an endocrine mode after partial hepatectomy in humans. METHODOLOGY: Portal blood was sampled through a catheter inserted through the umbilical vein to the portal trunk during surgery in 17 patients. Serum human hepatocyte growth factor levels were determined by enzyme-linked immunosorbent assay. RESULTS: Human hepatocyte growth factor levels were higher in portal than in peripheral serum throughout the study. Portal and peripheral serum human hepatocyte growth factor levels without complications increased rapidly and reached a maximum level 1 day after partial hepatectomy. The maximal level of portal and peripheral serum human hepatocyte growth factor was 1.20 and 1.00 ng/ml, respectively. In the case of hepatic failure after partial hepatectomy, portal and peripheral serum human hepatocyte growth factor levels markedly increased and reached 9.31 ng/ml and 6.78 ng/ml 2 days before death, respectively. CONCLUSIONS: These results suggest that hepatocyte growth factor increases in portal serum via an endocrine mode after partial hepatectomy in humans. Furthermore, measurement of the portal and peripheral serum human hepatocyte growth factor levels may be useful for the clinical evaluation of patients with post-operative hepatic failure.     

Type beta transforming growth factor reversibly inhibits the early proliferative response to partial hepatectomy in the rat.

Type beta transforming growth factor (TGF-beta), a factor produced by many cell types, is a potent inhibitor of hepatocyte DNA synthesis in vitro. To determine whether TGF-beta can influence hepatocyte proliferation in vivo, its effects were examined on the regenerative response of liver to partial hepatectomy (PH) in the rat. Porcine platelet-derived TGF-beta 1 (0.5 micrograms), administered intravenously at the time of PH and 11 hr later, reduced the fraction of hepatocytes engaged in DNA synthesis 22 hr after PH by 67% and inhibited the rate of hepatic [3H]thymidine incorporation by 50%. TGF-beta 2 produced a similar effect. A single dose of 0.5 micrograms of TGF-beta 1 given 11 hr after PH reduced liver [3H]thymidine incorporation by 32%; 4.5 micrograms of TGF-beta 1 or TGF-beta 2 inhibited DNA synthesis by 88% and the labeling index by 86%. Although sensitive to TGF-beta administered 11 hr after PH, late in the G1 phase of the cell cycle, a single dose of 0.5 micrograms given at the time of PH did not significantly influence DNA synthesis 22 hr after PH. The inhibitory effects of TGF-beta were transient; rats treated with two 0.5-microgram doses of TGF-beta at 0 and 11 hr had completely restored their original liver DNA mass 8 days after PH. Administration of 0.5 microgram of either TGF-beta 1 or TGF-beta 2 every 12 hr for 5 days failed to suppress the recovery of hepatic DNA mass. However, the nuclear labeling index of the TGF-beta-treated animals was significantly higher than that of the controls. There was no evidence of cytotoxicity from TGF-beta, as determined by liver histology and plasma concentrations of glucose, insulin-like growth factor I, and two hepatic enzymes. Thus, TGF-beta 1 and TGF-beta 2 reversibly inhibit the proliferative response of liver to PH and may be important in the modulation of normal liver growth and repair.     

Liver arterialization improves hepatocytes ultrastructure in rats with portacaval shunts

The effect of arterialization (ART) of the distal stump of the portal vein after portacaval shunt (PCS) on bile formation and liver ultrastructure was assessed. ART using the left gastric artery was performed in male Wistar rats. Animals were sacrificed 3 weeks later. ART prevented body and liver atrophy. However, the liver weight to body weight ratio was significantly decreased when compared to sham PCS (2.5±0.36 vs 3.22±0.15). Reduction in total bile secretion (μl/min) seen following PCS is reversed by ART. ART partly corrected hepatocyte size atrophy and the major ultrastructural abnormalities, namely the irregularity of the nucleus and the dilatation of the nuclear envelope and of the rough endoplasmic reticulum appearing after PCS. However, mitochondria remained swollen, deformed, and enlarged with scission figures. No lesions in connection with ART were seen. This result confirms, at the ultrastructural level, the beneficial effect of ART in PCS.     

Heparin-binding growth factor type 1 (acidic fibroblast growth factor): a potential biphasic autocrine and paracrine regulator of hepatocyte regeneration.

Heparin-binding growth factor type 1 (HBGF-1; sometimes termed acidic fibroblast growth factor) is potentially an important factor in liver regeneration. HBGF-1 alone (half-maximal effect at 60 pM) stimulated hepatocyte DNA synthesis and bound to a high-affinity receptor (Kd = 62 pM; 5000 per cell). Epidermal growth factor (EGF) neutralized or masked the mitogenic effect of HBGF-1 concurrent with appearance of low-affinity HBGF-1 binding sites. HBGF-1 reduced the inhibitory effect of transforming growth factor type beta (TGF-beta) on the EGF stimulus. Nanomolar levels of HBGF-1 decreased the EGF stimulus. An increase in hepatic HBGF-1 gene expression after partial hepatectomy precedes increases in expression of the EGF homolog, TGF-alpha, and nonparenchymal-cell-derived TGF-beta in the regenerating liver. Expression of HBGF-1 mRNA occurs in both hepatocytes and nonparenchymal cells and persists for 7 days in liver tissue after partial hepatectomy. HBGF-1 acting through a high-affinity receptor is a candidate for the early autocrine stimulus that drives hepatocyte DNA synthesis prior to or concurrent with the EGF/TGF-alpha stimulus. It may allow hepatocyte proliferation to proceed in the presence of low levels of TGF-beta. An EGF/TGF-alpha-dependent change in HBGF-1 receptor phenotype and increasing levels of nonparenchymal-cell-derived HBGF-1 and TGF-beta may serve to limit hepatocyte proliferation.     

A blocking peptide for transforming growth factor-beta1 activation prevents hepatic fibrosis in vivo

BACKGROUND/AIMS: Thrombospondin-1 is a major activator of transforming growth factor-beta1 (TGF-beta1), and a peptide derived from the latency-associated peptide, Leu-Ser-Lys-Leu (LSKL), inhibits the activation of TGF-beta1. In this study, the effects of LSKL on the hepatocyte damage and fibrogenesis in dimethylnitrosamine (DMN)-induced rat liver fibrosis were examined. METHODS: Animals were given an intraperitoneal (i.p.) injection of DMN or saline three times per week for 4 weeks, and treated with LSKL, a control peptide, or saline i.p. daily. RESULTS: Liver atrophy caused by DMN-injection was significantly inhibited in the DMN+LSKL group. The degrees of necrosis/degeneration and fibrosis scores were significantly lower in the DMN+LSKL group than in the control groups. The hydroxyproline content was significantly higher in the control groups than in the DMN+LSKL group. The amount of active TGF-beta1 was less in the DMN+LSKL group than in the control groups, and the active/total TGF-beta1 ratio in the DMN+LSKL group was suppressed in the control groups. Phosphorylation of Smad 2 in the liver was significantly decreased in the DMN+LSKL group. CONCLUSIONS: The LSKL peptide prevented the progression of hepatic damage and fibrosis through the inhibition of TGF-beta1 activation and its signal transduction in vivo.     

The effects of arterialisation of the portal stump on liver function and hepatic haemodynamics in cirrhotic rats with a portacaval shunt

Liver blood flow (xenon-133 clearance method) and wedged hepatic venous pressure were studied in cirrhotic rats immediately after and 3 weeks following portacaval shunting (PCS), PCS and arterialisation of the portal stump with the left gastric artery (PCS-ART) or sham operation. Liver weight and function were compared 3 weeks after operation. Liver blood flow and wedged hepatic venous pressure were significantly reduced immediately after and 3 weeks following PCS. PCS-ART maintained liver blood flow and wedged hepatic venous pressure within the pre-operative range and prevented the liver atrophy and deterioration in liver function observed in rats with PCS. The results suggest that arterialisation of the portal vein with an artery which does not significantly increase sinusoidal pressure may be of benefit in preventing the early undersirable sequelae of PCS in man.     

Transforming growth factor-beta and hepatocyte transdifferentiation in liver fibrogenesis

Currently, hepatic stellate cells (HSC) are thought to be the major fibrotic precursor cells that transdifferentiate to fibrogenic, extracellular matrix producing myofibroblasts in inflammatory liver tissue upon transforming growth factor-beta (TGF-beta) signaling, whereas hepatocytes are thought to respond with apoptosis to this cytokine. Starting out from in vitro experiments with primary hepatocyte cultures and immortalized AML-12 cells, TGF-beta signaling in this cell type was assessed and apoptosis was found to be only a minor effect. Instead, hepatocytes undergo epithelial mesenchymal transition (EMT), a physiological process in embryogenesis and of relevance for cancerous cell transformation. In injured liver, however, this process contributes to the promotion of fibrosis. Already after a few days of culture, hepatocytes lose their epithelial honeycomb-like shape towards a fibroblast-like phenotype. We could demonstrate by microarray analysis that stimulation of hepatocytes with TGF-beta regulates the expression of genes involved in EMT and fibrosis. Among these were, for example, Snail, a known mediator of EMT, and connective tissue growth factor (CTGF), a strong inducer of fibrosis. In a mouse model, hepatocyte-specific overexpression of Smad7 was able to blunt a fibrogenic response after CCl(4) intoxication. These results emphasize the dynamic nature of liver fibrosis, challenge the paradigm of HSC as a crucial source of liver myofibroblasts and hint towards a prominent role for hepatocytes in liver fibrogenesis.     

转化生长因子—β受体I及mRNA在慢性乙型肝炎肝组织中的表达及临床意义

目的研究转化生长因子-β受体Ⅰ（transforminggrowthfactor-βreceptorⅠ,TGF-βRⅠ）及其mRNA在慢性乙型肝炎（chronichepatitisB,CHB）肝组织中的表达及与肝组织病理改变和临床的关系。方法采用免疫组织化学及核酸原位杂交等技术观察了48例CHB患者肝组织中TGF-βRⅠ及其mRNA的表达。结果TGF-βRⅠ表达于肝细胞、窦内皮细胞及胆管上皮细胞,以肝细胞为主,呈细颗粒型及胞膜型分布。随肝组织炎症程度及纤维化程度加重,TGF-βRⅠ表达增强,相关系数分别为0.7095（P＜0.05）和0.6915（P＜0.05）。连续切片同步观察发现TGF-βRⅠmRNA与其受体蛋白的表达在阳性细胞数量及分布上基本一致。TGF-βRⅠ的表达与TBil（r＝0.3396,P＜0.05）、PA（r＝-0.3430,P＜0.05）及ALB（r＝-0.4173,P＜0.01）明显相关。结论TGF-βRⅠ在CHB肝损伤过程中可能起一定作用。     

Transforming growth factor beta and activin tonically inhibit DNA synthesis in the rat liver.

The present study was conducted to assess the role of transforming growth factor beta (TGF-beta) and activin(s) in the regulation of the mass of the liver. To this end, we eliminated TGF-beta or activin signaling in intact rat liver by adenovirus-mediated transfer of the gene encoding truncated type II TGF-beta receptor (AdextTR) or truncated type II activin receptor (AdextAR). In intact rat liver that received a single application of either AdextTR or AdextAR via the portal vein, DNA synthesis as assessed by bromodeoxy uridine (BrdU) labeling was induced. In AdextTR- or AdextAR-treated rats, nuclear labeling was significantly higher than that in AdexLacZ, adenovirus vector encoding Escherichia coli beta-galactosidase gene, or saline-treated rats at 3, 5, 7, and 9 days of infusion. The peak of the BrdU labeling was observed after 7 days of infusion and the labeling decreased thereafter. Apoptosis of hepatocytes, assessed by the terminal deoxynucleotidyl transferase (TdT)-mediated, dUTP-biotin nick-end labeling method was detected after 9 days of infusion. Immunoreactivity of TGF-beta and activin A increased in the liver after the blockade of the activin or TGF-beta signaling. TGF-beta and activin A may have been up-regulated when the action of these ligands was blocked. These results indicate that blockade of the action of either TGF-beta or activin leads to the initiation of DNA synthesis in intact liver. TGF-beta and activin tonically inhibit hepatocyte growth even in intact liver and may play a critical role in the maintenance of constant liver mass.     

Apoptosis of hepatic stellate cells: involvement in resolution of biliary fibrosis and regulation by soluble growth factors

BACKGROUND: Activated hepatic stellate cells (HSC) are central to the pathogenesis of liver fibrosis, both as a source of fibrillar collagens that characterise fibrosis and matrix degrading metalloproteinases and their tissue inhibitors, the TIMPs. AIMS: To test the hypothesis that HSC apoptosis is critical to recovery from biliary fibrosis and that soluble growth factors may regulate HSC survival and apoptosis. METHODS: Rats (n=15) were subjected to bile duct ligation for 21 days, after which biliodigestive anastomosis was undertaken (n=13). Livers were harvested at fixed time points of recovery for periods of up to 42 days. Numbers of activated HSCs were quantified after alpha smooth muscle actin staining and HSC apoptosis was detected by terminal UDP-nick end labelling (TUNEL) staining and quantified at each time point. HSC apoptosis was quantified in vitro in the presence or absence of insulin-like growth factor (IGF)-1, IGF-2, platelet derived growth factor (PDGF), and transforming growth factor beta1 (TGF-beta1). RESULTS: Following biliodigestive anastomosis after 21 days of bile duct ligation, rat liver demonstrated a progressive resolution of biliary fibrosis over 42 days, associated with a fivefold decrease in activated HSC determined by alpha smooth muscle actin staining. TUNEL staining indicated that loss of activated HSC resulted from an increase in the rate of apoptosis during the first two days post biliodigestive anastomosis. Serum deprivation and culture in the presence of 50 microM cycloheximide was associated with an increase in HSC apoptosis which was significantly inhibited by addition of 10 ng/ml and 100 ng/ml IGF-1, respectively (0.05>p, n=5). In contrast, 1 and 10 ng/ml of TGF-beta1 caused a significant increase in HSC apoptosis compared with serum free controls (p<0.05, n=4). PDGF and IGF-2 were neutral with respect to their effect on HSC apoptosis. CONCLUSION: HSC apoptosis plays a critical role in the spontaneous recovery from biliary fibrosis. Both survival and apoptosis of HSC are regulated by growth factors expressed during fibrotic liver injury.     

Hepatocyte growth factor gene transfer with naked plasmid DNA ameliorates dimethylnitrosamine-induced liver fibrosis in rats

Aim: Hepatocyte growth factor (HGF) has various biological properties, including antifibrogenic activity. In the present study, we tested the efficacy of HGF gene therapy using naked plasmid DNA in dimethylnitrosamine (DMN)-induced liver fibrosis in a rat model. Methods: Naked plasmid DNA encoding human HGF was injected once, together with a hypertonic solution, into the hepatic artery after DMN treatment on three consecutive days per week for 3 weeks. Naked plasmid DNA encoding beta-galactosidase was injected similarly in the DMN-treated control rats. DMN treatment was continued once weekly after gene transfer for additional 3 weeks. Results: The human HGF protein expression was detected in livers transfected with human HGF naked plasmid DNA, gradually decreasing by day 21. The expression of the endogenous rat HGF protein was also upregulated after human HGF gene transfer. Phosphorylation of c-Met, a HGF receptor, was detected only in livers transfected with human HGF plasmid DNA. Fibrosis was attenuated significantly in livers transfected with the human HGF plasmid. Attenuation wasaccompanied by decreased expression of alpha-smooth muscle actin. Increased portal vein pressure after treatment with DMN was suppressed significantly by HGF gene transfer. The upregulated hepatic protein expression of transforming growth factor-beta (TGF-beta) in response to DMN was markedly attenuated by HGF gene transfer accompanied by the increased protein expression for matrix metalloproteinases (MMP)-3 and -13. Conclusion: The hepatic arterial injection of human naked plasmid HGF DNA was effective in suppressing liver fibrosis induced in rats by DMN. The mechanisms by which HGF expression attenuated liver fibrosis may include the suppression of hepatic TGF-beta expression and the induction of MMP expression.