Vascular endothelial growth factor does not improve liver regeneration and survival after 90% subtotal liver resection

Vascular endothelial growth factor protein and gene delivery by novel nanomaterials for promoting liver regeneration after partial hepatectomy

Partial hepatectomy (PH) can lead to severe complications, including liver failure, due to the low regenerative capacity of the remaining liver, especially after extensive hepatectomy. Liver sinusoidal endothelial cells (LSECs), whose proliferation occurs more slowly and later than hepatocytes after PH, compose the lining of the hepatic sinusoids, which are the smallest blood vessels in the liver. Vascular endothelial growth factor (VEGF), secreted by hepatocytes, promotes LSEC proliferation. Supplementation of exogenous VEGF after hepatectomy also increases the number of LSECs in the remaining liver, thus promoting the reestablishment of the hepatic sinusoids and accelerating liver regeneration. At present, some shortcomings exist in the methods of supplementing exogenous VEGF, such as a low drug concentration in the liver and the reaching of other organs. More-over, VEGF should be administered multiple times and in large doses because of its short half-life. This review summarized the most recent findings on liver regeneration and new strategies for the localized delivery VEGF in the liver.

Study of DNA synthesis and mitotic activity of hepatocytes and its relation to angiogenesis in hepatectomised tumour bearing mice

Partial hepatectomy (PH) alters serum concentrations of substances involved in cellular proliferation, leading to the compensatory liver hyperplasia. Furthermore, angiogenesis is mainly stimulated by vascular endothelial growth factor (VEGF) and is a fundamental requirement either in liver regeneration or in tumours growth. This study looks at the expression of VEGF, DNA synthesis (DNAs) and mitotic activity (MA) in hepatectomised (H) and hepatectomised-tumour bearing (HTB) mice throughout a 24 h period. Adult male mice were sacrificed every 4 h from 26 to 50 h post-hepatectomy. H mice show a circadian rhythm in VEGF expression with a maximum value of 2.6 ± 0.1 at 08/46 h of day/hours posthepatectomy (HD/HPH); in DNAs, the maximum value was 3.4 ± 0.3 at 16/30 (HD/HPH) and in MA it was 2.3 ± 0.01 at 12/50 (HD/HPH). In HTB animals the peak of VEGF expression appears at 16/30 (HD/HPH) with a maximum value of 3.7 ± 0.1, the peak of DNAs was at 00/38 (HD/HPH) with a value of 4.6 ± 0.3 and the maximum value of MA of 08/46 (HD/HPH) with a value of 3.01 ± 0.3. We can conclude that the presence of the tumour induces modifications in the intensity and the temporal distribution of the circadian curves of VEGF expression, DNAs and MA of hepatectomised animals.

Administration of anti-vascular endothelial growth factor antibody following hepatectomy does not inhibit remnant liver regeneration or growth of remnant metastases

In addition to the use of chemotherapeutic agents for the prevention of multiple liver metastases from colorectal cancer, the anti-vascular endothelial growth factor (VEGF) antibody, bevacizumab, is often used, and its effectiveness has been established. By contrast, it has been reported that the use of bevacizumab prior to or following surgery delays wound healing or liver regeneration. In this study, we investigated whether the administration of bevacizumab following hepatectomy inhibits remnant liver regeneration or the growth of remnant metastases. Mice were partially hepatectomized (31% of the liver was removed), transplanted with the murine colorectal cancer cell line, CT26, in the remnant lobe, and intraperitoneally injected with bevacizumab (4 mg/kg) for a total of 6 times. Serum VEGF levels were measured on day 1 following surgery, and each lobe of the liver was weighed on day 14. Serum VEGF levels in non-hepatectomized, tumor-bearing mice exceeded those in their non-tumor-bearing counterparts; however, the administration of bevacizumab did not reduce the serum VEGF levels. The volume of the liver lobe of the hepatectomized, CT26-transplanted and non-CT26-transplanted mice was 1,349.6 and 735.5 mg, respectively, indicating rapid growth of the CT26 transplant (p=0.023). The volume of the CT26-transplanted lobe of the bevacizumab-administered mice was 1,379.0 mg, which was not significantly different from that (1,349.6 mg) of the non-bevacizumab-administered mice. The volume of the remnant lobe of the bevacizumab-administered mice was 1,051.0 mg, which did not significantly differ from that (957.3 mg) of the non-bevacizumab-administered mice. The administration of bevacizumab following hepatectomy did not delay remnant liver regeneration, and did not suppress the growth of metastases in the remnant lobes or remnant liver regeneration.

Expression of placental growth factor in regenerating livers after partial hepatectomy in the rat

BACKGROUND/AIMS

Placental growth factor (PlGF) is known for its role in pathological conditions to protect parenchymal cells of different organs from injury, whereas its presence in the liver and its potential importance in stimulating liver regeneration has never been described. This was investigated in this study using a rat model of partial hepatectomy (PH).

METHODS

The rat model of 70, 80, and 90% PH was used. Liver samples were taken peroperatively, 1 h, 1, 2, 3, and 7 days after surgery. Liver regeneration was evaluated by liver weight/body weight ratio, liver regeneration rate (%), and proliferating cell marker Ki67. The expression of PlGF, vascular endothelial growth factor (VEGF), VEGF receptor 1 (Flt-1), VEGF receptor 2 (Flk-1), and hypoxia inducible factor-1α mRNA was measured by quantitative real-time PCR and localized by immunohistochemistry.

RESULTS

The mRNA expression of PlGF was upregulated immediately after PH. Compared with 70 and 80% PH groups, the 90% PH group had a significantly lower PlGF and hypoxia inducible factor-1α mRNA expression, in parallel to a delayed liver weight/body weight ratio recovery. Only little differences were observed in VEGF, Flt-1, and Flk-1 mRNA expression among the PH groups.

CONCLUSION

This study shows for the first time the PlGF upregulation in regenerating livers, which is related to hypoxia stimulation and liver growth. The swift PlGF upregulation immediately after PH may indicate an important role for the PlGF/Flt-1 pathway in the early stage of liver regeneration.

Extent of liver resection modulates the activation of transcription factors and the production of cytokines involved in liver regeneration

AIM: To investigate the molecular events involved in liver regeneration following subtotal hepatectomy (SH) as previous studies have largely focused on partial hepatectomy (PH).

METHODS: Male Wistar rats were subjected to 70% PH or 90% SH, respectively, and sacrificed at different times after surgery. Untreated and sham-operated animals served as controls. Serum and liver samples were obtained to investigate liver function, apoptosis (TUNEL assay) and transcription factors (NF-κB, Stat3; ELISA) or cytokines (HGF, TNF-α, IL-6, TGF-α, TGF-β; quantitative RT-PCR) involved in liver regeneration.

RESULTS: Serum levels of ALT and AST in animals with 70% PH differed significantly from sham-operated and control animals. We found that the peak concentration 12 h after surgery returned to control levels 7 d after surgery. LDH was increased only at 12 h after 70% PH compared to sham. Bilirubin showed no differences between the sham and 70% resection. After PH, early NF-κB activation was detected 12 h after surgery (313.21 ± 17.22 ng/mL), while there was no activation after SH (125.22 ± 44.36 ng/mL) compared to controls (111.43 ± 32.68 ng/mL) at this time point. In SH, however, NF-κB activation was delayed until 24 h (475.56 ± 144.29 ng/mL). Stat3 activation was similar in both groups. These findings correlated with suppressed and delayed induction of regenerative genes after SH (i.e. TNF-α 24 h postoperatively: 2375 ± 1220 in 70% and 88 ± 31 in 90%; IL-6 12 h postoperatively: 2547 ± 441 in 70% and 173 ± 82 in 90%). TUNEL staining revealed elevated apoptosis rates in SH (0.44% at 24 h; 0.63% at 7 d) compared to PH (0.27% at 24 h; 0.15% at 7 d).

CONCLUSION: The molecular events involved in liver regeneration are significantly influenced by the extent of resection as SH leads to suppression and delay of liver regeneration compared to PH, which is associated with delayed activation of NF-κB and suppression of proregenerative cytokines.

Significance of portal venous VEGF during liver regeneration after hepatectomy

BACKGROUND

Although some studies have hypothesized portal venous blood is important for liver regeneration, no studies have established organs whose venous effluent flow into the portal vein secrete liver regenerating factors into the portal vein during liver regeneration. The aim of this study was to elucidate up-regulation of vascular endothelial growth factor (VEGF) in the portal vein, and expressions of hepatic regenerating factors in organs whose venous effluent flows into the portal vein during liver regeneration.

MATERIALS AND METHODS

VEGF protein in systemic and portal venous blood, as well as expression of VEGF, hypoxia-inducible factor-1alfa (HIF-1alpha), hepatocyte growth factor (HGF), and HGF activator (HGFA) mRNA were evaluated in the regenerating liver, spleen, and intestine following 70% partial hepatectomy (PHx) in rats.

RESULTS

The portal VEGF protein level was significantly higher than the systemic level post-PHx (portal/systemic at 72, 120, and 168 h post-PHx: 17.2/13.0, 20.2/12.8, and 24.0/14.7 pg/mL; P = 0.003, P = 0.022 and P = 0.032, respectively). VEGF mRNA expressions were significantly higher in the liver (P = 0.000027: 168 h), spleen (P = 0.000059: 72 h) and intestine (P = 0.01: 24-72 h) post-PHx compared with pre-PHx. HIF-1alpha, HGF, and HGFA mRNA expressions in the liver, intestine, and spleen were also significantly higher post-PHx compared to pre-PHx.

CONCLUSIONS

Portal VEGF was significantly higher than systemic VEGF, and expressions of VEGF, HIF-1alpha, HGF, and HGFA mRNA in the liver, spleen and intestine were also up-regulated during liver regeneration. These results suggest that hepatic regenerating factors derived from the spleen or intestine may contribute liver regeneration.