Inhibition of VEGF receptor-2 decreases the development of hyperdynamic splanchnic circulation and portal-systemic collateral vessels in portal hypertensive rats

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Background/Aims

Portal hypertension is characterized by the development of a hyperdynamic splanchnic circulation. To determine whether this process is angiogenesis-dependent, we assessed the effects of SU5416, a specific inhibitor of VEGF receptor-2, in portal hypertensive rats.

Methods

Rats with portal hypertension induced by partial portal vein ligation were treated with SU5416 or vehicle during 5 days. Then, hemodynamic studies were performed using radioactive microspheres. Protein expressions of CD31, VEGF receptor-2 and VEGF were also determined by Western blotting.

Results

Treatment of portal hypertensive rats with SU5416 resulted in a significant and marked decrease (by 44%) in portal venous inflow, and increases in splanchnic arteriolar resistance (by 68%) and portal venous resistance (by 93%). In addition, SU5416 administration significantly inhibited the formation of portal-systemic collateral vessels (52% inhibition), as well as the splanchnic CD31 and VEGF receptor-2 protein expressions in portal hypertensive rats, compared with those receiving vehicle.

Conclusions

This study demonstrates that the development of hyperdynamic splanchnic circulation and the formation of portal-systemic collateral vessels in portal hypertensive rats are angiogenesis-dependent processes that can be markedly inhibited by blockade of the VEGF signaling pathway. Therefore, modulation of angiogenesis may represent a potential target in the treatment of portal hypertension.

Introduction

Portal hypertension is one of the more common and severe complications that develop in patients with chronic liver diseases. Development of a hyperdynamic splanchnic circulatory state is a major component of the portal hypertensive syndrome. The increase in blood flow in splanchnic organs draining into the portal vein, and the subsequent increase in portal venous inflow, aggravates and perpetuates the portal hypertensive syndrome, especially when portal-systemic collaterals are extensive [1]. The mechanisms underlying this splanchnic hyperemia are not fully understood, but it has been shown that it is associated with an overproduction of endogenous vasodilators and decreased vascular reactivity to vasoconstrictors [1].

An intriguing possibility is that an increased formation of splanchnic blood vessels through an angiogenic process could also be involved in the maintenance of a hyperdynamic splanchnic circulation in portal hypertension. This hypothesis is based on our recent findings demonstrating the presence of increased splanchnic angiogenesis in a murine model of portal hypertension, and the involvement of this neovascularization on the formation of portal-systemic collateral blood vessels in portal hypertensive animals [2]. In the present study, we determined the hypothesis that hyperdynamic splanchnic circulation in portal hypertension is, at least in part, a vascular endothelial growth factor (VEGF)-dependent angiogenic process by assessing the hemodynamic effects of a specific inhibitor of VEGF receptor-2 in portal hypertensive rats.

Section snippets

Materials

SU5416 was provided by Sugen, Inc. (South San Francisco, California). Rabbit polyclonal antibodies against rat CD31, VEGF receptor-2 and VEGF, as well as the enhanced chemiluminescence western blotting system were from Santa Cruz Biotechnology (Santa Cruz, CA). Horseradish peroxidase-conjugated anti-rabbit IgG was from Stressgen (Sidney, Canada). 85Sr-labeled and 51Cr-labeled microspheres were from Perkin-Elmer (Boston, MA). Protein assay kit, and nitrocellulose membranes were from Bio-Rad

Results

SU5416 treatment was well tolerated, and no mortality was observed after daily treatment at 20 mg kg−1 day−1 for 5 days. The average body weight at the time of the studies was similar in the two groups of portal hypertensive rats: 293±19 g in the vehicle group versus 305±10 g in the SU5416 group (P=0.6).

Blockade of VEGFR-2 by SU5416 markedly attenuated the splanchnic hyperdynamic circulation observed in portal hypertensive rats. Thus, portal venous inflow was significantly decreased (by 44%) in PPVL

Discussion

The present study demonstrates that VEGF-dependent angiogenesis markedly contributes to both the development of hyperdynamic splanchnic circulation and the formation of portal-systemic collateral blood vessels, two major components of the portal hypertensive syndrome. Thus, our results show that antagonization of the VEGF/VEGFR-2 signaling pathway, by administration of SU5416 [4], [5], [6], [7], significantly decreased portal venous inflow (44% inhibition), and increased splanchnic arteriolar

Acknowledgements

This work was supported in part by grants from the Ministerio de Ciencia y Tecnologia (SAF2002-01461) and Instituto de Salud Carlos III (PI02739 and CO3/02). M.F. is the recipient of a contract from the Programa Ramon y Cajal, Ministerio de Ciencia y Tecnologia. We thank Dr Carlos Piera and Nieves Campos for technical assistance, Dr Raul Mendez for helpful discussions, and Sugen Inc. for providing the VEGFR-2 inhibitor SU5416.

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